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The Branner Geological Library 



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OPEN-AIE STUDIES 

AN INTRODUCTION TO GEOLOGY 

OUT-OF-DOOES 



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AN INTEODUCTION TO GEOLOGY 

OUT-OF-DOOES. 



BY 



GRENVILLE A. J. COLE, M.R.I.A., F.G.S, 

PROFESSOR OF QEOLOGY IN THE ROYAL COLLEGE OF 
SCIBNOB FOR IRELAND ; 

AUTHOR OF "AIDS IN PRACTICAL GEOLOGY" AND 
" THE GYPSY ROAD." 



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LONDON: 
CHAELES GEIFFIN AND COMPANY, Limited 

PHILADELPHIA : J. B. LIPPINCOTT COMPANY 

1895. 



208463 






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• • • • 
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• * 



Prinfed hy Ballantyne, Hanson & Co. 
At the Ballantyne Press 



TO 

RICHARD WHATELY DICKINSON 

This little book was in my mind all the time that 
we were studying together. So I dedicate it to you, 
and to all those who like seeing things for them- 
selves in the open air, 

GRENVILLE A, J, COLE, 



PREFACE 



Now that the elements of chemistry and physics are at 
last taking their place in the fundamental courses of self- 
respecting schools, we may fairly hope that a large number 
of persons will grow up with an intelligent interest in the 
world around them. In the first chapter of this book, I 
have gone lightly over some of the ground covered by 
such earlier lessons; and I take heart from the fact that 
Mr. Small, in his excellent little work, "The Earth," has 
felt it incumbent upon him to make the same reminders. 
I then ask the reader to step boldly forth into the outer air. 
In our walks abroad, we may be struck by this or that detail, 
seemingly trivial in itself, which finally leads up to some one 
of the vexed problems of the globe. Even in so simple a 
book as this, I have not spared references to sources of infor- 
mation, abroad as well as at home ; for one of the great incen- 
tives in scientific life is the knowledge that in all countries 
our fellow-observers are ready, and that our friends are con- 
stant in their aid. I have tried to deal in a sufficiently wide 
spirit with the special districts that are referred to, so that 
the observations may be transferred and applied to the im- 
mediate surroundings of the reader, or to the scenery of his 
summer holidays. Now-a-days, when cycling is so frequent 
and so free a means of travel, the geography and geology of 
nearer Europe have become keen realities to many of us, and 
almost all the references to landscapes in these chapters are 
the outcome of journeys on the road. 

I have wilfully mingled metric and English measurements 
throughout the book, since it seems that in this way alone we 
may hope to render popular the refined system of our neigh- 
bours, a system too often restricted to purely technical works. 
Maps, moreover, form an important part of the equipment 
of an observer in the field ; and outside our islands we soon 



VII 



viii PREFACE 

learn to think in kilometres per centimetre when studying 
their various scales. 

The great aim of this little book is to keep in view the 
fact that geology, like true zoology and true botany, is a 
study of the open air. To dissect a rabbit in the laboratory 
is a more intellectual exercise than to shoot him as he runs 
across the sand-hills ; but the object of such study, after all, 
is the understanding of the rabbit when alive. The average 
sportsman, with a careful eye for the habits of an animal, 
may at times go nearer towards this end than the average 
student at his microscope; and, similarly, it is only by a 
combination of two types of observation that a sound geologist 
can be made. Almost all great progress in natural know- 
ledge has thus been made by those who have seen and 
travelled, by those, in fact, who have studied in Nature's 
roofless school. 

Any person can now put himself in communication 
with his local field-club, in whatever quarter he may settle, 
and can thus receive the guidance of specialists in almost 
every county of our islands. For help in the many illus- 
trations, which have been kept before me or which have 
been actually reproduced in these pages, I am indebted 
largely to active members of the Geologists' Association — ^to 
Dr. Tempest-Anderson, Prof. Johnston-Lavis, Mr. Henry 
Preston, Mr. E. P. Ridley, and Mr. P. Woolnough ; while the 
work of that true artist, Mr. Welch of Belfast, has added 
greatly to any interest which the book may now possess. I 
can only give my thanks for such good-fellowship and assist- 
ance, and may perhaps hope in turn to be of some service to 
my friends. It is especially pleasant to me to include two 
plates from my Father's series of geological photographs, 
which formed perhaps my earliest introduction to the study 
of geology out-of-doors. 

GRENVILLE A. J. COLE. 

Dublin, May 1895. 



TABLE OF CONTENTS 



CHAP. 

I. THE MATERIALS OF THE EARTH 
II. A MOUNTAIN- HOLLOW 



IIL DOWN THE VALLEY 



IV. ALONG THE SHORE 



V. ACROSS THE PLAINS 



VI. DEAD VOLCANOES 



VIL A GRANITE HIGHLAND 



VIII. THE ANNALS OF THE EARTH 



IX. THE SURREY HILLS . 



X. THE FOLDS OF THE MOUNTAINS 



PAGE 

I 

28 

58 

87 
121 

148 

189 

216 

244 

283 



INDEX 



314 



IX 



LIST OF ILLUSTEATIONS 



FULL-PAGE ILLUSTRATIONS 



GwM-QLAS, Pass of Llanbebis 



PLATE 

I. Waterfall forming an Alcove in Stratified Bocks, 

Glencar, Go. Sligo 

II. Snow-fiUed Cirque at the base of the Matterhom, 
Switzerland 

III. Stratified Sands and Gravels, Antrim 

IV. The Sea breaking on a rocky coast, near Bally- 

castle, Go. Antrim 

V. The Grater-rim of the Puy de Pariou, Auvergne . 
YI. Golumns at the Giant's Gauseway, Go. Antrim, in 

Basaltic Lava-flow . . . . 
VIL Dyke of Dolerite, Quarry on Gave Hill, Belfast 
VIII. Columnar and massive Lava-flows at Pleaskin Head, 

Go. Antrim 

IX. Granite exposed on slope above the Eilkeel River, 

Mourne Mountains, Go. Down .... 

X. Fossil Shells in Pliocene Sands, Felixstowe, Suffolk . 

XI. Contorted Upper Jurassic Strata, Stare Gove, Lul- 

worth, Dorsetshire 



FrontUpiece 



To face page 42 



56 
76 

96 
150 

172 
181 

183 

190 
220 



}> 



284 



ILLUSTRATIONS IN TEXT 



FIG. PAGE 

1. Pot-hole, Glenariff, Go. Antrim 31 

2. Section illustrating the origin of Springs 59 

3. Section showing principle of Artesian Springs and Wells, and 

origin of Bournes 60 

4. Section of Gorge choked with Alluvium 75 

5. Section showing a slope of i in 17 79 

xi 



xii U8T OF ILLUSTRATIONS 

m. PAOB 

6. Sections of Alpine valley and Sootoh glens 83 

7. Old Lake-Terraoes of the Salt- Lake area of Utah '139 

8. The island of Vuloano in eruption 155 

9. Small Cones thrown up on Etna 159 

la Section of a Volcano 161 

11. Floating Scoriso above the Submarine Eruption off Fantelleria . 163 

12. Microscopic section of Obsidian 165 

13. Microscopic section of Basalt 167 

14. The Puy de Lassolas and the Fuy de la Vache .... 176 

15. Oeological Map, showing Lava-flows descending from Puys in 

Auvergne 177 

i6w Granite Pinnacles, Moume Mountains 193 

17. Unconformable Junction, with Overlap and Overstep . .219 

18. Internal cast of a Cerithium, Portland Stone .... 221 

19. a, Pecten Beaverl ; h. Peoten einctus ; r. Pecten idandicus . 225 

ja Trilobites 235 

«i. Section across the Surrey Hills 249 

ftt. Section illustrating Variation of Width of Outcrop 253 

t^ Sand with Spicules of Siliceous Sponges, Hythe Beds, Surrey . 261 

•4* Aneylooeras gigas 269 

ft$k AcatUKoceras rothomagense 271 

Mk AeUnocamax plenua 273 

i|. InoararMM Cuvieri 274 

tS^ Section illustrating Fan-Structure in a Mountain-Chain 284 

t^ Section illustrating Recumbent Folds 284 

j^x Section across a Fault 285 

%ts Plan of a Fault in inclined Strata 286 

Jf V Ridges and Valleys formed by Folds in the Jura Mountains . 291 
%%. Recumbent Synclinal and Folding on the Windgalle . -297 






* • 

* • • ' 



OPEN-AIR STUDIES 



CHAPTER I 

THE MATERIALS OF THE EARTH 

When we were children, as soon as we could think and 
ask questions, most of us tried to find out two important 
matters — how to make things, and what things are made of. 
The little boy who cut open his drum to see where the sound 
came from was not so entirely foolish as is sometimes repre- 
sented, for he at least made an interesting and valuable 
experiment. He learnt in this way that a drum was best 
constructed by stretching two thin skins opposite to one 
another, and shutting in a quantity of air between them. 
He was not satisfied with the mere showy outsides of things, 
or with the royal arms of Great Britain and Ireland painted 
on the wooden barrel of the drum. He felt that the sound', 
which was the great feature of the instrument, must have a 
cause ; and he set to work to find out something about it for 
himself. Probably he only got as far as seeing how the 
drum was made, and had to ask his father for the reason of 
this particular arrangement. But that is what every one has 
to do, and why no great discovery is likely to be of use to 
us unless we know what other people have previously dis- 
covered. In the same way, we cannot write a passably useful 
book unless we are near the 50,000 volumes of a well-stocked 
public library. Our knowledge in this world does not go on 
by jumps and bounds, but by a study of what others have 
seen and done, and of the records of their failure or success. 
Even if, after a long series of experiments, we have to leave 
our old drums damaged and cut open, we may soon have wit 
enough to make newer and better ones for the service of 
ourselves and our descendants. 

A 



2 OPEN-AIR STUDIES 






Ii\' edirfy times, it was most important that man should 
find but how to make things. He had to build shelters 
agairisjK'the rain; he had to find weapons with which to 
cqn2b4^ ^^^ wild beasts ; he had to carve out gourds into 
Y^sljiftls in which liquids could be carried. But all these 
.thifrgs were by no means easy, and required a good deal of 
\o!?servation. Nature was already doing many wonderful 
:'V tilings in the great world round about, and it was well to 
'.. 'watch, and even to imitate, these closely. After all, what- 
• • ever was required by man had to be made out of natural 
materials. One result of this struggle with diflSculties was 
that early man took to studying the stones beneath his feet. 
Some of his earliest instruments were made of stone ; and 
we know that many savage tribes have only given up the 
use of stone axes and stone arrow-heads since the arrival of 
European traders on their coasts. Primitive peoples would 
soon observe that some kinds of stone break more easily 
than others, that some kinds can be chipped in almost any 
direction so as to give a sharp cutting edge, and that some, 
again, are far superior in hardness or durability to the 
rest. It became important to search among the rocks for 
materials suited to each special purpose ; and thus began, 
perhaps, the first researches into the structure of the world 
around us. 

When native metals were discovered, and when, moreover, 
it was found that valuable substances could be extracted by 
heat from stones utterly unlike them in appearance, the 
study of the earth became a much more complicated matter ; 
and at last a few thoughtful persons took to inquiring how 
such-and-such materials, used by man in the manufacture of 
common things, came themselves to be made in the heart of 
the old solid earth. Then began the science of Gteology, the 
systematic study of the way in which the world is built up, 
and of the natural changes which go on within it and upon it. 
Even the earliest men must have seen that the earth 
changed around them. Floods came down, and covered 
smiling landscapes with sand and stones from distant hills ; 
volcanoes broke out, and heaped ashes and lava upon the 
surface j the sea worked against the land, and washed the 
coast steadily away ; while in other places tawny rivers wan- 
dered through the plains and thrust their burden of mud in 
long banks far to seaward. 




THE MATERIALS OF THE EARTH 3 

Thus the earth changed its surface, growing at one 
place, decaying away at another ; and men began to realise 
that it had a history, beside which their own lives were short 
indeed. And yet it is only in the last hundred years or so 
that we have been able to read this history at all clearly, 
and even now we understand only that end of it which lies 
nearest to ourselves. 

Before we go out and try to read a page or two of this 
history, we must learn something of the materials with 
which we have to deal. Of what, then, is the earth actually 
made? 

As a matter of fact, we know only a very small part of 
the vast globe on which we live. The centre of the earth 
lies 4000 miles beneath us, and our mines and borings pene- 
trate the great mass to a depth of only about a mile. But, 
as we shall see later, the outer layers of the earth have 
become wrinkled and folded, so that rocks which once lay 
far below the surface have been brought up within our 
reach. Hence in some places, immediately under the loose 
soil, we may find materials which were formerly ten or 
fifteen miles lower down; and this enables us to say that 
we have some idea of the constitution of the globe to a 
depth of fifteen miles from the surface. It is not much, 
this mere outer shell, fifteen miles thick all round the 
earth; but it is all we shall have to deal with, and we 
speak of this accessible region as the crust of the earth. 

This solid crust is made of rocks. Any workman in a 
quarry will tell us, for instance, that granite is a rock, or 
that sandstone is a rock. But, when we examine these two 
materials, we see that they are made up of distinct particles 
which themselves are worth inquiring into. The granite 
has clear little lumps, like glass, in it ; and dull white or 
pink bodies, which seem to break across in a regular manner, 
with smooth or step- like surfaces ; and soft flaky things 
which reflect the light brilliantly, and which can be pulled 
away, or dag out with a knife, in the form of little shining 
plates. The sandstone, on the other hand, is made of 
practically one kind of material throughout, in the form of 
a number of hard and somewhat rounded grains. 

In each case we call these constituents, having characters 
of their own, the minerals which compose the rock. The 
granite consists of at least three distinct minerals, the sand- 




4 OPEN- AIR STUDIES 

stone of only one. Now, if we break up a rock, and select 
a number of fragments of any one kind of mineral, a chemist 
will show us that this mineral is itself made up of certain 
chemical substances, which he can separate and accui*ately 
determine. He will be able to find out in what proportions 
these chemical substances are present, and will thus give us 
an account of the chemical constitution of the mineral. 

But what about these various substances? They may 
be stated by our friendly chemist to be chemical compounds, 
and these can be further split up into their elements. Or, to 
take the simplest case, our mineral may possibly consist of 
merely one element. 

Here we may remind ourselves of some of our chemical 
notions. We must go back, indeed, to the foundations of 
several sciences for the correct understanding of our rocks, 
and this first chapter is going to be a serious one, before we 
can fairly get out into the country and the open air. But 
we must remember that all the things with which we shall 
deal are quite natural, all come from the earth itself that 
stretches round us ; and those parts of chemistry and physics 
which are possibly a little dull to us seem so merely because 
we cannot handle or directly observe the things about which 
we are being told. If we could see the tiny ** atoms " 
moving in the ** molecule " of a substance, we should pro- 
bably be as delighted and as fascinated as if we were sitting 
on a mountain-peak and watching the great balance of the 
stars. 

A chemical element is a substance that cannot be split 
up, by any means at present in our power, into any other 
substances with different properties from those by which it 
is itself characterised. It is thus the simplest kind of 
material known to us. Gold, silver, copper, and iron are 
elements; sulphur is an element; so also is carbon, well 
known to us in its commonest form, the " black-lead " of 
our pencils. There are now about seventy elements known, 
and others, at present doubtful, are likely to be added to 
the list 

The ancients regarded the earth as an element in itself, 
something existing as a foundation for other things, the 
remaining elements being air, fire, and water. What we 
ow know as elements were often treated in earlier times 
yaried forms of the same fundamental material ; but all 



THE MATERIALS OF THE EARTH S 

experiment has shown us up to the present that there are 
really, in this earth and throughout the mighty universe, a 
number of different kinds of matter. To be quite simple in 
our conceptions, we might wish to say that all elements are 
made up of different arrangements of particles of one first- 
formed matter ; but that would be merely guess-work, and 
at present we cannot get beyond our seventy elements. 

If we conceive the smallest particle of an element that 
can independently exist, we may call such a particle an 
atom. It will have a certain weight, and the atoms of 
different elements differ in their weights. But any quantity 
of matter that we can see, even with a microscope, must 
consist of enormous numbers of atoms. 

The atoms are said to be grouped together in molecules, 
or " little masses." Chemists regard the molecule of certain 
elements as consisting of only one atom ; in others, two or 
even six atoms may form the molecule. A molecule has 
been defined by Professor Tilden as " the smallest quantity 
which is able to take part in or result from a chemical 
change." ^ 

A chemical compound is built up of molecules, each of 
which consists of atoms of more than one kind. In the 
simplest compounds the molecule consists of only two 
atoms, one atom of one element being combined with one 
of another. The elements have been shown to combine 
together in fixed proportions, forming compounds with dis- 
tinctive properties. We may hence say that the molecule 
of a compound is the smallest particle into which the sub- 
stance could be divided while yet retaining its peculiar 
chemical constitution. Further splitting might give us cer- 
tain simpler compounds; but ultimately the actual atoms, 
or groups of similar atoms, of each molecule would be set 
free ; in other words, the compound would separate into 
its elements. 

All this may seem beyond human observation ; but large 
quantities of molecules of a compound can be dealt with in 
our experiments, and large quantities of elementary molecules 
can be extracted by chemical processes from them. Or, on 
the other hand, we can cause large quantities of elementary 
molecules of different kinds to combine together to form 
large quantities of molecules of a chemical compound ; and 

^ "Introduction to the Study of Chemical Philosophy,** 1876, p. 4. 



6 OPEN-AIR STUDIES 

in either case, by weighing the qnaotity of each snbstance 
dealt with, we can find oat in what proportions the elemente 
are combined in any particnlar componnd. 

We may now glance backwards, and define an atom as the 
smallest qnantity of an element that can be driven ont of or 
caused to enter into a molecule of a compound in the subtle 
process of destroying or producing any of the known chemical 
combinations of that element. Here we have got down as 
far as we can go in the chemical constitution of a mineral. 
Minerals are made of chemical substances, which are mode 
of molecules ; these molecules cousist of atoms either (a) of 
different kinds, in which case we are dealing with a com- 
pound, or (i) of only one kind, in which case our substance 
IS an element. 

Now we may try to arrive at a definition of a mineral. 
Let us look at those which we have separated from the 
granite — three materials evidently requiring distinct names, 
evidently differing markedly in their physical characters. 

The clear little lumps are called Q^iartz, and do not tell ns 
very much by their external appearance. They break across 
with irregular curving fractures, much as glass does ; and 
they have in this case no regular shape. But they are trans- 
parent, and also very hard; for we cannot scratch them 
with a knife, and they, on the other hand, will scratch glass. 
Moreover, they will not soften and melt, as glass does, when 
held with a pair of forceps in the dame of a Bunsen burner 
— the gas-burner used in chemical laburatorit's or in ordinary 
gas-stovea Clearly, they are not grains of glass. 

If we give them to a chemist, he will find in them the two 
elements, Silicon and Oxygen, always in the proportion of one 
atom of sUicon to two atoms of oxygen. Quartz is made, in 
fact, of the oxide of silicon, commonly called Silica. We may 
take any of these grains from granite rocks found anywhere J 
in the world, and yet their chemical composition will be iT ' 
same. 

The dull white or pink bodies ai-e called Orthorln/tr-^ nrJ 
Orthoclase Felspar ; these, as we have already notiffi ' 
the property of breaking across regularly 
tions — in two directions, at any rate— i^ 
hammer. This shows that their inte 
in which the molecules u" 
that of qnartz. Moreovi 



THE MATERIALS OF THE EARTH 7 

external shape; it is often regular, and, even on roughly- 
broken surfaces of the rock, the larger orthoclases are seen 
to approach the form of small flat bricks. Then, in turning 
about the rock-specimen in the hand, some of these ortho- 
clases seem to be built up of two parts ; that is, one half of 
the orthoclase catches the light and gives a bright reflection, 
while the other half looks dull ; clearly the planes of fracture 
are differently sloped in the two parts of the mineral, and it 
has not a perfectly simple internal structure. 

A good knife will just scratch the orthoclase, if drawn 
firmly across it ; but orthoclase will scratch ordinary glass ; 
we thus learn that it is harder than glass, but not so hard as 
quartz. A little splinter of orthoclase can just be melted 
after holding it for some time in the flame of a Bnnsen 
gas-burner. 

Our chemist tells us that this mineral is more complex 
than quartz. He finds in it Silicon, Oxygen, Aluminium, 
Potassium, and generally Sodium. The proportion of these 
elements to one another is always the same, except in the 
case of the two last named. Sometimes there is only potas- 
sium present, and no sodium ; sometimes sodium occurs, and 
then there is less potassium. We say that the potassium may 
be replaced in part by sodium without the principal charac- 
teristics of the mineral being altered. In such cases it must 
be a matter of general consent and judgment as to whether 
we are to call the mineral by a new name when such a re- 
placement occurs. The atoms of sodium are lighter than 
those of potassium ; but any difference in the weight of a 
given bulk of orthoclase, according as it contains potassium, 
or both potassium and sodium, would be very trifling. Cases 
often occur, moreover, where a lighter element replaces a 
heavier one, and yet the resulting variety of the mineral is 
actually heavier than the ordinary form. The molecules con- 
taining the lighter element must in such cases lie closer 
together, i.e., there must be more of them in a given space, 
than occurs when only molecules containing the heavier 
element are present. 

So we may note that the chemical composition of some 
minerals may vary slightly, varieties being set up which are 
grouped together under the common mineral name. A mole- 
cule of our typical orthoclase contains 2 atoms of potassium, 
2 of aluminium, 6 of silicon, and 1 6 of oxygen. But in most 



8 OPEN-AIR STUDIES 

specimens of orthoclase there are some molecules in which 
two atoms of sodium take the place of the two at»oms of potas- 
sium. When such molecules are shown by a chemical analysis 
to be numerous, we call the mineral variety Soda-Orthoclase. 

Our third mineral in the granite is called Mica — the plate- 
like substance which is easily dug out with the knife, and 
which gives such a shining appearance to many specimens of 
the rock. Some micas are pale and silvery ; others are quite 
dark, being bronze-coloured or black ; but they have many 
characters in common. Again and again their proper form 
can be seen ; their molecules are clearly capable of building 
up six-sided plates. This structure is so common that it can- 
not be accidental ; and careful measures show that the angles 
of the hexagonal figure are kept the same in the same chemical 
variety. Such a structure is called a crystal ; and a little 
observation will show us that the orthoclase also is in the 
form of crystals, though they have probably not been able to 
grow to such perfection. The mica splits very easily in one 
direction, so that we can flake off thin flexible plates ; and 
even the blacker micas are no longer opaque when one of their 
thin plates is held up to the light. The mineral is quite soft, 
and can often be scratched by the thumb-nail. 

The chemical composition of the micas is still more 
complex than that of the orthoclase felspar, but all common 
varieties contain Silicon, Oxygen, Aluminium, Potassium, 
Magnesium, Iron, and Hydrogen. The pale varieties con- 
tain little iron and usually little magnesium ; the dark 
varieties are richer in these elements and poorer in silicon 
and aluminium. There may be a good deal of replacement 
of one element by another in the mica series, the general 
external characters being retained ; and several different 
kinds or species of mica are recognised, and are known by 
distinct mineral names. 

If we are so fortunate as to find a granite with a number 
of small hollows in it, perhaps half-an-inch or an inch across, 
such as occur in the famous rocks of the northern part of 
the Mourne Mountains, then we may see that all the 
minerals which we have discussed are capable of forming 
crystals, wherever freedom is given to them and when they 
are not too much squeezed together. In such hollows we 
find the mica, and the orthoclase, and the quartz itself, 
delicately crystallised, beautifully and regularly shaped, so 



THE MATERIALS OF THE EARTH 9 

that persons looking at the handsome crystals in pnblic 
collections often think that they have been artificially cut 
and polished. But you have only to go into the hills, and 
search in cracks and hollows for yourselves, to find that 
crystals occur naturally, and that they are, indeed, the form 
frequently adopted by natural chemical substances. And, 
further, the crystals of one compound usually differ from 
those of another ; the sides make different angles one with 
another, even if the forms are very much alike; so that, 
by careful observation and measurement of the angles in 
various crystals, we can use the outer shape to help us in 
determining the nature of the mineral. 

And now we can at last arrive at our definition. A 

'mineral is a natural substance, formed without the action of 

plants or animals. Its chemical composition is constant, or 

vaHes only by a well-defined series of chemical replacements. 

Under favourable conditions, it assumes a crystalline form. 

One mineral is known from another by a number of 
characters which must be considered all together; and 
these will be found stated in any text-book of mineralogy.^ 
Let us run over the most important of these characters 
here. 

I . Colour. — When there are several minerals in a rock, 
this character often clearly marks out one from another. 
But it is of far less importance than might be supposed, 
since many common minerals are coloured by some trifling 
impurity; a sort of stain runs through them, as it were, 
and in their pure condition they are colourless. Metallic 
ores, however, usually have characteristic colours ; thus Iron 
Pyrites, the common iron sulphide, is brass-yellow, and 
Native Copper, the natural element, is copper-red. But, on 
the other hand, the red gem Euby and the blue Sapphire are 
mere varieties of the same mineral species, Corundum, the 
composition of both being aluminium oxide coloured by a 
substance very insignificant in amount.^ Hence we must 

^ Such as Hatch, "Mineralogy" (Whittaker & Co.) ; Rutley, "Mineralogy" 
(T. Murby). 

'^ Artificial corundum has been coloured red (ruby) by adding chromium 
fluoride to the materials employed ; and, curiously enough, the addition of 
this same substance in varying proportions has given rise to sapphires and to 
a green variety. Rubies have also been made by adding potassium bichro- 
mate, and sapphires by adding cobalt oxide (Fouqu^ and L^vy, Synthase 
des MiiUraux et des Roches, pp. 220 and 222). 



^^ iMaMMNiiqr ^^ O p Mity > — Some miiiends mre 
vlUiMi^'l^^^eilW^t^ lirtMMfft^HBit — in dun flakes, at any rale. 
Uv^^w 4^>i^ iiW|Hmliii!H^ and diemical changes as the mineral 
^^tlhMH vH^ vt^^s^ «^M9^ nHider a clear substance finally opaque. 
V'HtvHV ^shUvhmw earbonale) is typically transparent; Iron 
IN ^"ili^ V* v«f^ji^)U^ ^ven when groand down thinner than a 

,^x Lwlrt^ — Some minerals reflect light brilliantly, like 
\^u^'|« aiu) Koek«8alt> which are said to have a ''glassy 
)m)i|4V»'' kHH^Ui^ of their resemblance in this respect to glass. 
iHht^rt^ an Iron Pyrites, look like polished metal, and are 
^s\ ti> have a *' metallic lustre."' Others are quite dull and 
t^M'thy> like Wad, one of the hydrous manganese oxides. 

4. MaUeability and Barittleness. — Some minerals can 
lie hauauered out without breaking, and are said to be 
^MuaUeaWe,** as Native Gold. Others are brittle, and fly 
to pieot>H when struck, as Tron l^rites or Quartz. 

5, HardllMS. — ^This is one of the most important and 
UHefu) oliaraoters. A mineral may be brittle, and yet may 
he 8oft eni>ugh to be cut into with a knife, like Copper 
Pyrites (sulplade of copper and iron); or it may be brittle, 
t\\u\ yot too hanl to be scratched with a knife, like Iron 
l*yrite». For our present purposes, we may note three kinds 
ot hnnlnesH among unnerals : — 

ri. Koine unnerals cannot be scratched by a good knife. 
b. Some minerals can be scratched by a knife, but not 

by the thumb-nail, 
f. Some minerals can be scratched by the thumb-nail. 

Sometimes, in examining our rocks, it is difficult to 
say if some small projecting grain is hard or soft; we 
cannot determine whether we can scratch it, for fear of 
demolishing it or removing it altogether. In such cases 
we may draw it across the side of the knife-blade or across 
our thumb-nail, and see if it scratches either of these, in 
which case it is harder than the substance scratched. If 
the mineral is in the form of loose grains, like those broken 
from a sandstone, they can be stuck on to a piece of wood by 
^me firm cement, such as the old bicycle-tyre cement, with 
sharp little points sticking out above the surface ; and 




THE MATERIAI^ OF THE EARTH I I 

then, held by this handle, we can draw them across the 
knife or across the thumb-nail. Another plan is to squeeze 
them between two plates of glass, such as the slips used for 
mounting microscopic objects ; it is easy then to see whether 
the little grains are scratching the surface of the glass. 

6. Streak. — ^The colour of the powder of a mineral, 
produced by cutting into it or by crushing it out under 
a clean hammer upon white paper, is called its "streak." 
Every time that we use an ordinary pencil we see the 
streak of Graphite (one form of carbon), the mineral known 
popularly as " black-lead." 

7. Flexibility. — Some minerals can be bent, especially 
in thin flakes, and remain in the form thus given to them. 
They are then said to be "flexible." 

8. Elasticity. — Other minerals are said to be " elastic," 
when, like Mica, they spring back into their former shape 
after being bent. 

9. Specific Gravity. — The statement of the Specific 
Gravity of a substance expresses its relative weight as com- 
pared with pure water at a temperature — in most English 
experiments — of 60° F. If we say that a mineral has a 
specific gravity of 3, we mean that any given bulk of it 
is three times as heavy as an equal bulk of water at 
60° P. A cubic inch of it would thus weigh as much as 
three cubic inches of water at that temperature. Most 
minerals of common occurrence have a specific gravity be- 
tween 2 and 3.5. Meerschaum, used for the bowls of pipes, 
is as low as 1.5, while Gold is as high as 19.3, and a native 
alloy of Platinum and Iridium actually reaches 23. 

In the beautiful system of weights and measures in- 
vented in France, and now used by almost all civilised 
peoples, the specific gravity of a mineral or a rock at once 
tells us how much space a given weight of it will occupy, 
or, on the other hand, how much a given bulk of it will 
weigh. In this system the weight known as t gramme is the 
weight of a bulk of water occupying i cubic centimetre at a 
temperature of 4° C. Hence, adopting this temperature for 
the experiments, i gramme of a substance of a specific 
gravity of 5 will occupy i-Sth of a cubic centimetre, or 200 
cubic millimetres, and 100 grammes of it will occupy 20 
cubic centimetres. On the other hand, to take another 
example, 700 cubic centimetres of a mineral with a specific 



• ■ 



OPEN-AIR STUDIES 



"..' 



IiX' e^y times, it was most important that man should 
find but how to make things. He had to build shelters 
agauist'the rain; he had to find weapons with which to 
cqiill4t the wild beasts ; he had to carve out gourds into 
Vtesljials in which liquids could be carried. But all these 
.thin'gs were by no means easy, and required a good deal of 
'.ol^ervation. Nature was already doing many wonderful 
:'V things in the great world round about, and it was well to 
'•. Vatch, and even to imitate, these closely. After all, what- 
• • ever was required by man had to be made out of natural 
materials. One result of this struggle with difficulties was 
that early man took to studying the stones beneath his feet. 
Some of his earliest instruments were made of stone ; and 
we know that many savage tribes have only given up the 
use of stone axes and stone arrow-heads since the arrival of 
European traders on their coasts. Primitive peoples would 
soon observe that some kinds of stone break more easily 
than others, that some kinds can be chipped in almost any 
direction so as to give a sharp cutting edge, and that some, 
again, are far superior in hardness or durability to the 
rest. It became important to search among the rocks for 
materials suited to each special purpose ; and thus began, 
perhaps, the first researches into the structure of the world 
around ua 

When native metals were discovered, and when, moreover, 
it was found that valuable substances could be extracted by 
heat from stones utterly unlike them in appearance, the 
study of the earth became a much more complicated matter ; 
and at last a few thoughtful persons took to inquiring how 
such-and-such materials, used by man in the manufacture of 
common things, came themselves to be made in the heart of 
the old solid earth. Then began the science of Geology, the 
systematic study of the way in which the world is built up, 
and of the natural changes which go on within it and upon it. 
Even the earliest men must have seen that the earth 
changed around them. Floods came down, and covered 
smiling landscapes with sand and stones from distant hills ; 
volcanoes broke out, and heaped ashes and lava upon the 
surface ;: the sea worked against the land, and washed the 
coast steadily away ; while in other places tawny rivers wan- 
dered through the plains and thrust their burden of mud in 
long banks far to seaward. 



THE MATERIALS OF THE EARTH 3 

Thus the earth changed its surface, growing at one 
place, decaying away at another ; and men began to realise 
that it had a history, beside which their own lives were short 
indeed. And yet it is only in the last hundred years or so 
that we have been able to read this history at all clearly, 
and even now we understand only that end of it which lies 
nearest to ourselves. 

Before we go out and try to read a page or two of this 
history, we must learn something of the materials with 
which we have to deal. Of what, then, is the earth actually 
made? 

As a matter of fact, we know only a very small part of 
the vast globe on which we live. The centre of the earth 
lies 4000 miles beneath us, and our mines and borings pene- 
trate the great mass to a depth of only about a mile. But, 
as we shall see later, the outer layers of the earth have 
become wrinkled and folded, so that rocks which once lay 
far below the surface have been brought up within our 
reach. Hence in some places, immediately under the loose 
soil, we may find materials which were formerly ten or 
fifteen miles lower down ; and this enables us to say that 
we have some idea of the constitution of the globe to a 
depth of fifteen miles from the surface. It is not much, 
this mere outer shell, fifteen miles thick all round the 
earth; but it is all we shall have to deal with, and we 
speak of this accessible region as the crust of the earth. 

This solid crust is made of rocks. Any workman in a 
quarry will tell us, for instance, that granite is a rock, or 
that sandstone is a rock. But, when we examine these two 
materials, we see that they are made up of distinct particles 
which themselves are worth inquiring into. The granite 
has clear little lumps, like glass, in it ; and dull white or 
pink bodies, which seem to break across in a regular manner, 
with smooth or step-like surfaces ; and soft flaky things 
which reflect the light brilliantly, and which can be pulled 
away, or dug out with a knife, in the form of little shining 
plates. The sandstone, on the other hand, is made of 
practically one kind of material throughout, in the form of 
a number of hard and somewhat rounded grains. 

In each case we call these constituents, having characters 
of their own, the minerals which compose the rock. The 
granite consists of at least three distinct minerals, the sand- 



4 OPEN-AIR STUDIES 

stone of only one. Now, if we break up a rock, and select 
a number of fragments of any one kind of mineral, a chemist 
will show us that this mineral is itself made up of certain 
chemical substances, which he can separate and accurately 
determine. He will be able to find out in what proportions 
these chemical substances are present, and will thus give us 
an account of the chemical constitution of the mineral. 

But what about these various substances? They may 
be stated by our friendly chemist to be chemical compounds, 
and these can be further split up into their elements. Or, to 
take the simplest case, our mineral may possibly consist of 
merely one element. 

Here we may remind ourselves of some of our chemical 
notions. We must go back, indeed, to the foundations of 
several sciences for the correct understanding of our rocks, 
and this first chapter is going to be a serious one, before we 
can fairly get out into the country and the open air. But 
we must remember that all the things with which we shall 
deal are quite natural, all come from the earth itself that 
stretches round us ; and those parts of chemistry and physics 
which are possibly a little dull to us seem so merely because 
we cannot handle or directly observe the things about which 
we are being told. If we could see the tiny ** atoms " 
moving in the " molecule " of a substance, we should pro- 
bably be as delighted and as fascinated as if we were sitting 
on a mountain-peak and watching the great balance of the 
stars. 

A chemical element is a substance that cannot be split 
up, by any means at present in our power, into any other 
substances with different properties from those by which it 
is itself characterised. It is thus the simplest kind of 
material known to us. Gold, silver, copper, and iron are 
elements; sulphur is an element; so also is carbon, well 
known to us in its commonest form, the " black-lead '* of 
our pencils. There are now about seventy elements known, 
and others, at present doubtful, are likely to be added to 
the list. 

The ancients regarded the earth as an element in itself, 
something existing as a foundation for other things, the 
remaining elements being air, fire, and water. What we 
now know as elements were often treated in earlier times 
as varied forms of the same fundamental material ; but all 



\ 



THE MATERIALS OF THE EARTH S 

experiment has shown us up to the present that there are 
really, in this earth and throughout the mighty universe, a 
number of different kinds of matter. To be quite simple in 
our conceptions, we might wish to say that all elements are 
made up of different arrangements of particles of one first- 
formed matter ; but that would be merely guess-work, and 
at present we cannot get beyond our seventy elements. 

If we conceive the smallest particle of an element that 
can independently exist, we may call such a particle an 
atom. It will have a certain weight, and the atoms of 
different elements differ in their weights. But any quantity 
of matter that we can see, even with a microscope, must 
consist of enormous numbers of atoms. 

The atoms are said to be grouped together in molecules, 
or " little masses." Chemists regard the molecule of certain 
elements as consisting of only one atom ; in others, two or 
even six atoms may form the molecule. A molecule has 
been defined by Professor Tilden as " the smallest quantity 
which is able to take part in or result from a chemical 
change." ^ 

A chemical compound is built up of molecules, each of 
which consists of atoms of more than one kind. In the 
simplest compounds the molecule consists of only two 
atoms, one atom of one element being combined with one 
of another. The elements have been shown to combine 
together in fixed proportions, forming compounds with dis- 
tinctive properties. We may hence say that the molecule 
of a compound is the smallest particle into which the sub- 
stance could be divided while yet retaining its peculiar 
chemical constitution. Further splitting might give us cer- 
tain simpler compounds; but ultimately the actual atoms, 
or groups of similar atoms, of each molecule would be set 
free ; in other words, the compound would separate into 
its elements. 

All this may seem beyond human observation ; but large 
quantities of molecules of a compound can be dealt with in 
our experiments, and large quantities of elementary molecules 
can be extracted by chemical processes from them. Or, on 
the other hand, we can cause large quantities of elementary 
molecules of different kinds to combine together to form 
large quantities of molecules of a chemical compound ; and 

^ "Introduction to the Study of Chemical Philosophy," 1876, p. 4. 



4 OPEN-AIR STUDIES 

stone of only one. Now, if we break up a rock, and Belect 
a number of fragments of any one kind of mineral, a chemist 
will show us that this mineral is itself made up of certain 
chemical substances, which he can separate and accurately 
determine. He will be able to find out in what proportions 
these chemical substances are present, and will thus give us 
an account of the chemical constitution of the mineral. 

But what about these various substances? They may 
be stated by our friendly chemist to be chemical compounds, 
and these can be further split up into their elements. Or, to 
take the simplest case, our mineral may possibly consist of 
merely one element. 

Here we may remind ourselves of some of our chemical 
notions. We must go back, indeed, to the foundations of 
several sciences for the correct understanding of our rocks, 
and this first chapter is going to be a serious one, before we 
can fairly get out into the country and the open air. But 
we must remember that all the things with which we shall 
deal are quite natural, all come from the earth itself that 
stretches round us ; and those parts of chemistry and physics 
which are possibly a little dull to us seem so merely because 
we cannot handle or directly observe the things about which 
we are being told. If we could see the tiny " atoms " 
moving in the " molecule " of a substance, we should pro- 
bably be as delighted and as fascinated as if we were sitting 
on a mountain-peak and watching the great balance of the 
stars. 

A chemical element is a substance that cannot be split 
up, by any means at present in our power, into any other 
substances with different properties from those by which it 
is itself characterised. It is thus the simplest kind of 
material known to us. Gold, silver, copper, and iron are 
elements; sulphur is an element; so also is carbon, well 
known to us in its commonest form, the " black-lead " of 
our pencils. There are now about seventy elements known, 
and others, at present doubtful, are likely to be added to 
the list. 

The ancients regarded the earth as an element in itself, 
something existing as a foundation for other things, the 
remaining elements being air, fire, and water. What we 
now know as elements were often treated in earlier times 
as varied forms of the same fundamental material ; but all 



THE MATERIALS OF THE EARTH S 

experiment has shown us up to the present that there are 
really, in this earth and throughout the mighty universe, a 
number of different kinds of matter. To be quite simple in 
our conceptions, we might wish to say that all elements are 
made up of different arrangements of particles of one first- 
formed matter ; but that would be merely guess-work, and 
at present we cannot get beyond our seventy elements. 

If we conceive the smallest particle of an element that 
can independently exist, we may call such a particle an 
atom. It will have a certain weight, and the atoms of 
different elements differ in their weights. But any quantity 
of matter that we can see, even with a microscope, must 
consist of enormous numbers of atoms. 

The atoms are said to be grouped together in molecules, 
or ** little masses.'* Chemists regard the molecule of certain 
elements as consisting of only one atom ; in others, two or 
even six atoms may form the molecule. A molecule has 
been defined by Professor Tilden as " the smallest quantity 
which is able to take part in or result from a chemical 
change."^ 

A chemical compound is built up of molecules, each of 
which consists of atoms of more than one kind. In the 
simplest compounds the molecule consists of only two 
atoms, one atom of one element being combined with one 
of another. The elements have been shown to combine 
together in fixed proportions, forming compounds with dis- 
tinctive properties. We may hence say that the molecule 
of a compound is the smallest particle into which the sub- 
stance could be divided while yet retaining its peculiar 
chemical constitution. Further splitting might give us cer- 
tain simpler compounds; but ultimately the actual atoms, 
or groups of similar atoms, of each molecule would be set 
free ; in other words, the compound would separate into 
its elements. 

All this may seem beyond human observation ; but large 
quantities of molecules of a compound can be dealt with in 
our experiments, and large quantities of elementary molecules 
can be extracted by chemical processes from them. Or, on 
the other hand, we can cause large quantities of elementary 
molecules of different kinds to combine together to form 
large quantities of molecules of a chemical compound ; and 

^ "Introduction to the Study of Chemical Philosophy," 1876, p. 4. 



6 OPCX-AIR smffls^ 

VOL either oee* bj weiekiB|r tbe qvMitiiT of tmA sabfitanoe 
deah with, ve can fiad o«t in vkat propoitioiis the etemeotB 
aje combixfeed in aaj partkalar ocxnpcMind. 

We maj oo v giuce backwards^ and define an atom as the 
smaller qoanthr of an elemeiit thai can be driven ont of or 
caused to enter inlo a moleciile of a compound in the sobde 
prvKe«so£ detstrojiiig or prodocii^ any of the known chemical 
combinations of that elemient. Hei^ we have got down as 
far as we can go in the chemical ocmstitiition of a mineraL 
Minerals are made of chemical sobetances. whidi aie made 
of mdecales : thiK^ OKJecales consist of atoms either (a) of 
different kinds^ in which case we are dealing with a com- 
pounds or {b) of only one kind* in which case oar snbstance 
is an element. 

Now we may try to arrtTe at a definition of a mineraL 
Let us lo^>k at tho^ which we have separated from the 
^rnaiite — thr^v materials evidently reiiuiring distinct names, 
evidently differing markedly in their physical characters. 

The clear little lumps art^ called Quartz, and do not tell as 
very much by their external appearance. They break across 
with irrt^ular curving fractures* much as glass does; and 
they have in this case no regular shape. But they are trans- 
l>arent, and also Nvry hard; for we cannot scratch them 
with a knife, and they, on the other hand, will scratch glass. 
Moreiwer* they will not si^ften and melt, as glass does, when 
helil with a ^lair of forceps in the Hame of a Bunsen burner 
— the gas-burner used in chenucal laboratories or in ordinary 
g^»-»t4>vea. Clearly » they are not grains of glass. 

If we give them to a chemist, he will find in them the two 
^«n)«nta, ailiooii ai\d Oxygtni* always in the proportion of one 
•*Wi of ailioou to two atoms of oxygen. Quartz is made, iu 
lw» of the oxide of silicon, commonly called Silica. We may 
JJ^ W^ of thwe grains from granite rocks found anywhere 
to tht^ W€MrId> ai\d yet tlunr chenucal composition will be the 

^^llio dull white or pink boiUes are called Orthoclnse, or 
OWAiWiw^ >WqMir ; thest\ as we have already noticed, have 
J«^ pro)HMrty of breaking across regularly in certain direc- 
llonK— iu two directions, at any rate — when struck with a 
hMnmt^r, This dhows that their internal structure, the way 
to whioh tlie nioleoules are grouped together, differs from 
•'^^fc o' iimutiL Moraover. we can see something of their 




THE MATERIALS OF THE EARTH / 

external shape; it is often regular, and, even on roughly 
broken surfaces of the rock, the larger orthoclases are seen 
to approach the form of small flat bricks. Then, in turning 
about the rock-specimen in the hand, some of these ortho- 
clases seem to be built up of two parts ; that is, one half of 
the orthoclase catches the light and gives a bright reflection, 
while the other half looks dull; clearly the planes of fracture 
are differently sloped in the two parts of the mineral, and it 
has not a perfectly simple internal structure. 

A good knife will just scratch the orthoclase, if drawn 
firmly across it ; but orthoclase will scratch ordinary glass ; 
we thus learn that it is harder than glass, but not so hard as 
quartz. A little splinter of orthoclase can just be melted 
after holding it for some time in the flame of a Bunsen 
gas-burner. 

Our chemist tells us that this mineral is more complex 
than quartz. He finds in it Silicon, Oxygen, Aluminium, 
Potassium, and generally Sodium. The proportion of these 
elements to one another is always the same, except in the 
case of the two last named. Sometimes there is only potas- 
sium present, and no sodium ; sometimes sodium occurs, and 
then there is less potassium. We say that the potassium may 
be replaced in part by sodium without the principal charac- 
teristics of the mineral being altered. In such cases it must 
be a matter of general consent and judgment as to whether 
we are to call the mineral by a new name when such a re- 
placement occurs. The atoms of sodium are lighter than 
those of potassium ; but any difiFerence in the weight of a 
given bulk of orthoclase, according as it contains potassium, 
or both potassium and sodium, would be very trifling. Cases 
often occur, moreover, where a lighter element replaces a 
heavier one, and yet the resulting variety of the mineral is 
actually heavier than the ordinary form. The molecules con- 
taining the lighter element must in such cases lie closer 
together, i.e., there must be more of them in a given space, 
than occurs when only molecules containing the heavier 
element are present. 

So we may note that the chemical composition of some 
minerals may vary slightly, varieties being set up which are 
grouped together under the common mineral name. A mole- 
cule of our typical orthoclase contains 2 atoms of potassium, 
2 of aluminium, 6 of silicon, and 1 6 of oxygen. But in most 



8 OPEN-AIR STUDIES 

specimens of orthoclase there are some molecules in which 
two atoms of sodium take the place of the two atoms of potas- 
sium. When such molecules are shown by a chemical analysis 
to be numerous, we call the mineral variety Soda-Orthoclase. 

Our third mineral in the granite is called Mica — ^the plate- 
like substance which is easily dug out with the knife, and 
which gives such a shining appearance to many specimens of 
the rock. Some micas are pale and silvery ; others are quite 
dark, being bronze-coloured or black ; but they have many 
characters in common. Again and again their proper form 
can be seen ; their molecules are clearly capable of building 
up six-sided plates. This structure is so common that it can- 
not be accidental ; and careful measures show that the angles 
of the hexagonal figure are kept the same in the same chemical 
variety. Such a structure is called a crystal ; and a little 
observation will show us that the orthoclase also is in the 
form of crystals, though they have probably not been able to 
grow to such perfection. The mica splits very easily in one 
direction, so that we can flake off thin flexible plates ; and 
even the blacker micas are no longer opaque when one of their 
thin plates is held up to the light. The mineral is quite soft, 
and can often be scratched by the thumb-nail. 

The chemical composition of the micas is still more 
complex than that of the orthoclase felspar, but all common 
varieties contain Silicon, Oxygen, Aluminium, Potassium, 
Magnesium, Iron, and Hydrogen. The pale varieties con- 
tain little iron and usually little magnesium ; the dark 
varieties are richer in these elements and poorer in silicon 
and aluminium. There may be a good deal of replacement 
of one element by another in the mica series, the general 
external characters being retained ; and several different 
kinds or species of mica are recognised, and are known by 
distinct mineral names. 

If we are so fortunate as to find a granite with a number 
of small hollows in it, perhaps half-an-inch or an inch across, 
such as occur in the famous rocks of the northern part of 
the Mourn e Mountains, then we may see that all the 
minerals which we have discussed are capable of forming 
crystals, wherever freedom is given to them and when they 
are not too much squeezed together. In such hollows we 
find the mica, and the orthoclase, and the quartz itself, 
delicately crystallised, beautifully and regularly shaped, so 



THE MATERIALS OF THE EARTH 9 

that persons looking at the handsome crystals in public 
collections often think that they have been artificially cut 
and polished. But you have only to go into the hills, and 
search in cracks and hollows for yourselves, to find that 
crystals occur naturally, and that they are, indeed, the form 
frequently adopted by natural chemical substances. And, 
further, the crystals of one compound usually differ from 
those of another ; the sides make different angles one with 
another, even if the forms are very much alike; so that, 
by careful observation and measurement of the angles in 
various crystals, we can use the outer shape to help us in 
detennining the nature of the mineral. 

And now we can at last arrive at our definition. A 

mineral is a natural substance, formed without the action of 

plants or animals. Its chemical composition is constant, or 

varies only by a well-defined series of chemical replacements, 

IlTider favourable conditions, it assumes a crystalline form. 

One mineral is known from another by a number of 
characters which must be considered all together; and 
these will be found stated in any text-book of mineralogy.^ 
Let us run over the most important of these characters 
here. 

I. Oolour. — When there are several minerals in a rock, 
this character often clearly marks out one from another. 
But it is of far less importance than might be supposed, 
since many common minerals are coloured by some trifling 
impurity; a sort of stain runs through them, as it were, 
and in their pure condition they are colourless. Metallic 
ores, however, usually have characteristic colours ; thus Iron 
Pyrites, the common iron sulphide, is brass-yellow, and 
Native Copper, the natural element, is copper-red. But, on 
the other hand, the red gem Ruby and the blue Sapphire are 
mere varieties of the same mineral species. Corundum, the 
composition of both being aluminium oxide coloured by a 
substance very insignificant in amount.^ Hence we must 

^ Such as Hatch, "Mineralogy" (Whittaker & Co.) ; Rutley, "Mineralogy" 
(T. Murby). 

^ Artificial corundum has been coloured red (ruby) by adding chromium 
fluoride to the materials employed ; and, curiously enough, the addition of 
this same substance in varying proportions has given rise to sapphires and to 
a green variety. Rubies have also been made by adding potassium bichro- 
mate, and sapphires by adding cobalt oxide (Fouqu^ and Ldvy, SyntMse 
dea MirUraux et des Roches, pp. 220 and 222). 



lO OPEN-AIR STUDIES 

rely on other characters besides colour in the determining 
of a mineral species. 

2. Transpa»rency or Opacity. — Some minerals are 
characteristically transparent — in thin flakes, at any rate. 
Here, again, impurities, and chemical changes as the mineral 
alters or decays, may render a clear substance finally opaque. 
Calcite (calcium carbonate) is typically transparent; Iron 
Pyrites is opaque, even when ground down thinner than a 
sheet of notepaper. 

3. Lustre. — Some minerals reflect light brilliantly, like 
Quartz and Bock-Salt, which are said to have a "glassy 
lustre," because of their resemblance in this respect to glass. 
Others, as Iron Pyrites, look like polished metal, and are 
said to have a "metallic lustre." Others are quite dull and 
earthy, like Wad, one of the hydrous manganese oxides. 

4. Malleability and Brittleness. — Some minerals can 
be hammered out without breaking, and are said to be 
"malleable," as Native Gold. Others are brittle, and fly 
to pieces when struck, as Iron Pyrites or Quartz. 

5. Hardness. — This is one of the most important and 
useful characters. A mineral may be brittle, and yet may 
be soft enough to be cut into with a knife, like Copper 
Pyrites (sulphide of copper and iron) ; or it may be brittle, 
and yet too hard to be scratched with a knife, like Iron 
Pyrites. For our present purposes, we may note three kinds 
of hardness among minerals : — 

a. Some minerals cannot be scratched by a good knife. 
6. Some minerals can be scratched by a knife, but not 

by the thumb-nail. 
c. Some minerals can be scratched by the thumb-nail. 

Sometimes, in examining our rocks, it is difficult to 
say if some small projecting grain is hard or soft; we 
cannot determine whether we can scratch it, for fear of 
demolishing it or removing it altogether. In such cases 
we may draw it across the side of the knife-blade or across 
our thumb-nail, and see if it scratches either of these, in 
which case it is harder than the substance scratched. If 
the mineral is in the form of loose grains, like those broken 
from a sandstone, they can be stuck on to a piece of wood by 
some firm cement, such as the old bicycle-tyre cement, with 
their sharp little points sticking out above the surface ; and 



THE MATERIAI^ OF THE EARTH II 

then, held by this handle, we can draw them across the 
knife or across the thumb-nail. Another plan is to squeeze 
them between two plates of glass, such as the slips used for 
mounting microscopic objects ; it is easy then to see whether 
the little grains are scratching the surface of the glass. 

6. Streak. — ^The colour of the powder of a mineral, 
produced by cutting into it or by crushing it out under 
a clean hammer upon white paper, is called its "streak." 
Every time that we use an ordinary pencil we see the 
streak of Graphite (one form of carbon), the mineral known 
popularly as " black-lead." 

7. Flexibility. — Some minerals can be bent, especially 
in thin flakes, and remain in the form thus given to them. 
They are then said to be "flexible." 

8. Elasticity. — Other minerals are said to be " elastic," 
when, like Mica, they spring back into their former shape 
after being bent. 

9. Specific Gravity. — The statement of the Specific 
Gravity of a substance expresses its relative weight as com- 
pared with pure water at a temperature — in most English 
experiments — of 60° F. If we say that a mineral has a 
specific gravity of 3, we mean that any given bulk of it 
is three times as heavy as an equal bulk of water at 
60° P. A cubic inch of it would thus weigh as much as 
three cubic inches of water at that temperature. Most 
minerals of common occurrence have a specific gravity be- 
tween 2 and 3.5. Meerschaum, used for the bowls of pipes, 
is as low as 1.5, while Gold is as high as 19.3, and a native 
alloy of Platinum and Iridium actually reaches 23. 

In the beautiful system of weights and measures in- 
vented in France, and now used by almost all civilised 
peoples, the specific gravity of a mineral or a rock at once 
tells us how much space a given weight of it will occupy, 
or, on the other hand, how much a given bulk of it will 
weigh. In this system the weight known as t gramme is the 
weight of a bulk of water occupying i cubic centimetre at a 
temperature of 4° C. Hence, adopting this temperature for 
the experiments, i gramme of a substance of a specific 
gravity of 5 will occupy i-5th of a cubic centimetre, or 200 
cubic millimetres, and 100 grammes of it will occupy 20 
cubic centimetres. On the other hand, to take another 
example, 700 cubic centimetres of a mineral with a specific 



lO OPEN-AIR STUDIES 

re]y on other characters besides coloar in the determining 
of a mineral species. 

2. Transparency or Opacity. — Some minerals are 
oliaracteristically transparent — in thin flakes, at any rate. 
Here, again, imparities, and chemical changes as the mineral 
alters or decays, may render a clear subBtance finally opaqne. 
Calcite (calcium carbonate) is typically transparent; Iron 
Pyrites is opaque, even when ground down thinner than a 
sheet of notepaper. 

3. LlUti*e. — Some minerals reflect light brilliantly, like 
Quartz and Rock-Salt, which are said to have a "glaesy 
lustre," because of their resemblance in this respect to ^asa. 
Others, as Iron I^rites, look like polished metal, and are 
said to have a "metallic lustre." Others are quite dull and 
earthy, like Wad, one of the hydrous manganese oxides. 

4. Halleability and Brittleness. — Some minerals can 
be hammered ont without breaking, and are said to be 
"malleable," as Native Gold. Others are brittle, and fly 
to pieces when struck, as Iron Pyrites or Quartz. 

5. Hardness. — This is one of the most important and 
useful cliarocters. A mineral may be brittle, and yet may 
be soft enough to be cut into with a knife, like Copper 
Pyrites (sulphide of copper and iron) ; or it may be brittle, 
and yet too hard to be scratched with a knife, like Iron 
Pyrites. For our present purposes, we may note three kinds 
of hardness among minerals: — 

a. Some minerals cannot be scratched by a good knife. 

b. Some minerals can be scratched by a knife, but not 

by the thumb-nail. 

c. Some minerals can be scratched by the thnmb-niiL 

Sometimes, in examining our rocks, it is difficult to 
say it some small projecting grain is hard or soft; wo 
cannot determine whether wr can scratch it, for fear (rf j 
demolishing it or removing it altogether. In 1 
we may draw it across the side of tin? kuife-blade 
onr thumb-nail, and see if it scratches either j" 
which case it is harder than the substance I 
the mineral is in the form of loose grains, UJte'i 
from a sandstone, they can be stuck on 
some firm cement, such as th^ ' ' " 
their sharp little points stidE 




lO OPEN-AIR STUDIES 

rely on other characters besides colour in the determining 
of a mineral species. 

2. Transparency or Opacity. — Some minerals are 
characteristically transparent — in thin flakes, at any rate. 
Here, again, impurities, and chemical changes as the mineral 
alters or decays, may render a clear substance finally opaque. 
Calcite (calcium carbonate) is typically transparent; Iron 
Pyrites is opaque, even when ground down thinner than a 
sheet of notepaper. 

3. Lustre. — Some minerals reflect light brilliantly, like 
Quartz and Eock-Salt, which are said to have a "glassy 
lustre," because of their resemblance in this respect to glass. 
Others, as Iron Pyrites, look like polished metal, and are 
said to have a "metallic lustre." Others are quite dull and 
earthy, like Wad, one of the hydrous manganese oxides. 

4. Malleability and Brittleness. — Some minerals can 
be hammered out without breaking, and are said to be 
** malleable," as Native Gold. Others are brittle, and fly 
to pieces when struck, as Iron Pyrites or Quartz. 

5. Hardness. — This is one of the most important and 
useful characters. A mineral may be brittle, and yet may 
be soft enough to be cut into with a knife, like Copper 
Pyrites (sulphide of copper and iron) ; or it may be brittle, 
and yet too hard to be scratched with a knife, like Iron 
Pyrites. For our present purposes, we may note three kinds 
of hardness among minerals : — 

a. Some minerals cannot be scratched by a good knife. 
6. Some minerals can be scratched by a knife, but not 

by the thumb-nail, 
c. Some minerals can be scratched by the thumb-nail. 

Sometimes, in examining our rocks, it is difficult to 
say if some small projecting grain is hard or soft; we 
cannot determine whether we can scratch it, for fear of 
demolishing it or removing it altogether. In such cases 
we may draw it across the side of the knife-blade or across 
our thumb-nail, and see if it scratches either of these, in 
which case it is harder than the substance scratched. If 
the mineral is in the form of loose grains, like those broken 
from a sandstone, they can be stuck on to a piece of wood " 
some firm cement, such as the old bicycle-tyre oemf " ^ 
their sharp little points sticking oat above the ^ 




THE MATERIAI^ OF THK EARTH I I 

then, held by tliis handle, we can drew them across tlie 
knife or across the thumb-Doil. Another plan is to BCjuefKe 
them between two plates of glass, snch as the slips ased for 
mounting microscopic objects ; it is easj then to see whether 
the little greins are scratching the earface of the glass. 

6. Strealc — The colonr of the powder of a mineral, 
produced by cutting into it or by cmahins it out nnder 
a clean hammer upon white paper, is called its "streak." 
Every time that we nse an orainaiy pencil we see the 
streak of Graphite (one form of carbon), the mineral known 
popnl^y as " black-lead." 

7. Flexibility.^ Some minerals can be bent, especially 
in thin flakes, and remain in the form thus given to them. 
They are then said to be "flexible." 

8. Elasticity- — Other minerals are said to be " elastic," 
when, like Mico, they spring back into their former shapt' 
after being bent. 

9. Spedflc Gravity. — The statement of the Specific 
Gravity of a Bubstance expresses its relative weight OB com- 
pared with pure water at a temperature— in most English 
experiments — of 60° F. If we Bay that a mineral has a 
specific gravity of 3, we mean that any given bulk of it 
is three times as heavy as an equal bulk of water at 
60° F. A cubic inch of it would thus weigh as much as 
three cubic inches of water at that temperature. Miist 
minerals of common occurrence have 8 specific gravity be- 
tween 2 and 3.5. Meerschaum, used for the bowls of pipes, 
is as low as 1.5, while Gold is as high as 19-3, and a native 
alloy of Platinum and Iridium actually reaches 23. 

In the beautiful system of weights and measures in- 
vented in France, and now used % almost all civilised 
peoples, the specific gravity of a mineral or a rock at once 
tells U8 how much space a given weight of it will occupy, 
or, on the other hand, how much a given bulk of it will 
weigh. In this system the weight known as I gramme is the 
weight of a bulk of water occapyinK i cubic centimetre at a 

■ncf,, ad(.|ii.ing this temperature for 

imti of a substance of a specific 

[-5th of a cubic centimetre, or 200 

,'z!immf-H of it will occupy 20 

; otimr hand, to take another 

H of a mineral with a specific 




• '•, 



• "• 



2 OPEN-AIR STUDIES 

• • . 

Ii\' e^y times, it was most important that man should 
find biit how to make things. He had to build shelters 
agauisjb'the rain; he had to find weapons with which to 
cqnlh4t the wild beasts ; he had to carve out gourds into 
yes^s in which liquids could be carried. But all these 
ihin'gs were by no means easy, and required a good deal of 
•.ol^ervation. Nature was already doing many wonderful 
r'vinings in the great world round about, and it was well to 
*. Vatch, and even to imitate, these closely. After all, what- 
• • ever was required by man had to be made out of natural 
materials. One result of this struggle with diflSculties was 
that early man took to studying the stones beneath his feet. 
Some of his earliest instruments were made of stone ; and 
we know that many savage tribes have only given up the 
use of stone axes and stone arrow-heads since the arrival of 
European traders on their coasts. Primitive peoples would 
soon observe that some kinds of stone break more easily 
than others, that some kinds can be chipped in almost any 
direction so as to give a sharp cutting edge, and that some, 
again, are far superior in hardness or durability to the 
rest. It became important to search among the rocks for 
materials suited to each special purpose ; and thus began, 
perhaps, the first researches into the structure of the world 
around us. 

When native metals were discovered, and when, moreover, 
it was found that valuable substances could be extracted by 
heat from stones utterly unlike them in appearance, the 
study of the earth became a much more complicated matter ; 
and at last a few thoughtful persons took to inquiring how 
such-and-such materials, used by man in the manufacture of 
common things, came themselves to be made in the heart of 
the old solid earth. Then began the science of Gteology, tbe 
systematic study of the way in which the world is built up, 
and of the natural changes which go on within it and upon it. 
Even the earliest men must have seen that the earth 
changed around them. Floods came down, and covered 
smiling landscapes with sand and stones from distant hills ; 
volcanoes broke out, and heaped ashes and lava upon the 
surface ;; the sea worked against the land, and washed tbe 
coast steadily away ; while in other places tawny rivers wan- 
dered through the plains and thrust their burden of mud in 
long banks far to seaward. 



THE MATERIALS OF THE EARTH 3 

Thus the earth changed its surface, growing at one 
place, decaying away at another ; and men began to realise 
that it had a history, beside which their own lives were short 
indeed. And yet it is only in the last hundred years or so 
that we have been able to read this history at all clearly, 
and even now we understand only that end of it which lies 
nearest to ourselves. 

Before we go out and try to read a page or two of this 
history, we must learn something of the materials with 
which we have to deal. Of what, then, is the earth actually 
made? 

As a matter of fact, we know only a very small part of 
the vast globe on which we live. The centre of the earth 
lies 4CXX) miles beneath us, and our mines and borings pene- 
trate the great mass to a depth of only about a mile. But, 
as we shall see later, the outer layers of the earth have 
become wrinkled and folded, so that rocks which once lay 
far below the surface have been brought up within our 
reach. Hence in some places, immediately under the loose 
soil, we may find materials which were formerly ten or 
fifteen miles lower down ; and this enables us to say that 
we have some idea of the constitution of the globe to a 
depth of fifteen miles from the surface. It is not much, 
this mere outer shell, fifteen miles thick all round the 
earth ; but it is all we shall have to deal with, and we 
speak of this accessible region as the crust of the earth. 

This solid crust is made of rocks. Any workman in a 
quarry will tell us, for instance, that granite is a rock, or 
that sandstone is a rock. But, when we examine these two 
materials, we see that they are made up of distinct particles 
which themselves are worth inquiring into. The granite 
has clear little lumps, like glass, in it ; and dull white or 
pink bodies, which seem to break across in a regular manner, 
with smooth or step- like surfaces ; and soft flaky things 
which reflect the light brilliantly, and which can be pulled 
away, or dug out with a knife, in the form of little shining 
plates. The sandstone, on the other hand, is made of 
practically one kind of material throughout, in the form of 
a number of hard and somewhat rounded grains. 

In each case we call these constituents, having characters 
of their own, the minerals which compose the rock. The 
granite consists of at least three distinct minerals, the sand- 



* • 



OPEN-AIR STUDIES 



• * 



Ii\' e^y times, it was most important that man shonld 
find but how to make things. He had to build shelters 
againsj^' the rain; he had to find weapons with which to 
cqnlb4t the wild beasts ; he had to carve out gourds into 
yes^s in which liquids could be carried. But all these 
ihin'gs were by no means easy, and required a good deal of 
•.ol^ervation. Nature was already doing many wonderful 
7.*tnings in the great world round about, and it was well to 
.'watch, and even to imitate, these closely. After all, what- 
• ever was required by man had to be made out of natural 
materials. One result of this struggle with diflSculties was 
that early man took to studying the stones beneath his feet. 
Some of his earliest instruments were made of stone ; and 
we know that many savage tribes have only given up the 
use of stone axes and stone arrow-heads since the arrival of 
European traders on their coasts. Primitive peoples would 
soon observe that some kinds of stone break more easily 
than others, that some kinds can be chipped in almost any 
direction so as to give a sharp cutting edge, and that some, 
again, are far superior in hardness or durability to the 
rest. It became important to search among the rocks for 
materials suited to each special purpose ; and thus began, 
perhaps, the first researches into the structure of the world 
around us. 

When native metals were discovered, and when, moreover, 
it was found that valuable substances could be extracted by 
heat from stones utterly unlike them in appearance, the 
study of the earth became a much more complicated matter ; 
and at last a few thoughtful persons took to inquiring how 
such-and-such materials, used by man in the manufacture of 
common things, came themselves to be made in the heart of 
the old solid earth. Then began the science of Geology, the 
systematic study of the way in which the world is built up, 
and of the natural changes which go on within it and upon it. 
Even the earliest men must have seen that the earth 
changed around them. Floods came down, and covered 
smiling landscapes with sand and stones from distant hills ; 
volcanoes broke out, and heaped ashes and lava upon the 
surface ;; the sea worked against the land, and washed the 
coast steadily away ; while in other places tawny rivers wan- 
dered through the plains and thrust their burden of mud in 
long banks far to seaward. 



THE MATERIALS OF THE EARTH 3 

Thus the earth changed its surface, growing at one 
place, decaying away at another ; and men began to realise 
that it had a history, beside which their own lives were short 
indeed. And yet it is only in the last hundred years or so 
that we have been able to read this history at all clearly, 
and even now we understand only that end of it which lies 
nearest to ourselves. 

Before we go out and try to read a page or two of this 
history, we must learn something of the materials with 
which we have to deal. Of what, then, is the earth actually 
made? 

As a matter of fact, we know only a very small part of 
the vast globe on which we live. The centre of the earth 
lies 4CXX) miles beneath us, and our mines and borings pene- 
trate the great mass to a depth of only about a mile. But, 
as we shall see later, the outer layers of the earth have 
become wrinkled and folded, so that rocks which once lay 
far below the surface have been brought up within our 
reach. Hence in some places, immediately under the loose 
soil, we may find materials which were formerly ten or 
fifteen miles lower down; and this enables us to say that 
we have some idea of the constitution of the globe to a 
depth of fifteen miles from the surface. It is not much, 
this mere outer shell, fifteen miles thick all round the 
earth ; but it is all we shall have to deal with, and we 
speak of this accessible region as the crust of the earth. 

This solid crust is made of rocks. Any workman in a 
quarry will tell us, for instance, that granite is a rock, or 
that sandstone is a rock. But, when we examine these two 
materials, we see that they are made up of distinct particles 
which themselves are worth inquiring into. The granite 
has clear little lumps, like glass, in it ; and dull white or 
pink bodies, which seem to break across in a regular manner, 
with smooth or step- like surfaces ; and soft flaky things 
which reflect the light brilliantly, and which can be pulled 
away, or dug out with a knife, in the form of little shining 
plates. The sandstone, on the other hand, is made of 
practically one kind of material throughout, in the form of 
a number of hard and somewhat rounded grains. 

In each case we call these constituents, having characters 
of their own, the minerals which compose the rock. The 
granite consists of at least three distinct minerals, the sand- 



4 OPEN-AIR STUDIES 

stone of only one. Now, if we break up a rock, and select 
a number of fragments of any one kind of mineral, a chemist 
will show us that this mineral is itself made up of certain 
chemical substances, which he can separate and accurately 
determine. He will be able to find out in what proportions 
these chemical substances are present, and will thus give us 
an account of the chemical constitution of the mineral. 

But what about these various substances? They may 
be stated by our friendly chemist to be chemical compounds, 
and these can be further split up into their elements. Or, to 
take the simplest case, our mineral may possibly consist of 
merely one element. 

Here we may remind ourselves of some of our chemical 
notions. We must go back, indeed, to the foundations of 
several sciences for the correct understanding of our rocks, 
and this first chapter is going to be a serious one, before we 
can fairly get out into the country and the open air. But 
we must remember that all the things with which we shall 
deal are quite natural, all come from the earth itself that 
stretches round us ; and those parts of chemistry and physics 
which are possibly a little dull to us seem so merely because 
we cannot handle or directly observe the things about which 
we are being told. If we could see the tiny ** atoms " 
moving in the " molecule " of a substance, we should pro- 
bably be as delighted and as fascinated as if we were sitting 
on a mountain-peak and watching the great balance of the 
stars. 

A chemical element is a substance that cannot be split 
up, by any means at present in our power, into any other 
substances with different properties from those by which it 
is itself characterised. It is thus the simplest kind of 
material known to us. Gold, silver, copper, and iron are 
elements; sulphur is an element; so also is carbon, well 
known to us in its commonest form, the " black-lead " of 
our pencils. There are now about seventy elements known, 
and others, at present doubtful, are likely to be added to 
the list. 

The ancients regarded the earth as an element in itself, 
something existing as a foundation for other things, the 
remaining elements being air, fire, and water. What we 
now know as elements were often treated in earlier times 
as varied forms of the same fundamental material ; but all 



THE MATERIALS OF THE EARTH 5 

experiment has shown us up to the present that there are 
really, in this earth and throughout the mighty universe, a 
number of difiEerent kinds of matter. To be quite simple in 
our conceptions, we might wish to say that all elements are 
made up of difiEerent arrangements of particles of one first- 
formed matter ; but that would be merely guess-work, and 
at present we cannot get beyond our seventy elements. 

If we conceive the smallest particle of an element that 
can independently exist, we may call such a particle an 
atom. It will have a certain weight, and the atoms of 
difiEerent elements difiEer in their weights. But any quantity 
of matter that we can see, even with a microscope, must 
consist of enormous numbers of atoms. 

The atoms are said to be grouped together in molecules, 
or " little masses." Chemists regard the molecule of certain 
elements as consisting of only one atom ; in others, two or 
even six atoms may form the molecule. A molecule has 
been defined by Professor Tilden as " the smallest quantity 
which is able to take part in or result from a chemical 
change." ^ 

A chemical compound is built up of molecules, each of 
which consists of atoms of more than one kind. In the 
simplest compounds the molecule consists of only two 
atoms, one atom of one element being combined with one 
of another. The elements have been shown to combine 
together in fixed proportions, forming compounds with dis- 
tinctive properties. We may hence say that the molecule 
of a compound is the smallest particle into which the sub- 
stance could be divided while yet retaining its peculiar 
chemical constitution. Further splitting might give us cer- 
tain simpler compounds; but ultimately the actual atoms, 
or groups of similar atoms, of each molecule would be set 
free ; in other words, the compound would separate into 
its elements. 

All this may seem beyond human observation ; but large 
quantities of molecules of a compound can be dealt with in 
our experiments, and large quantities of elementary molecules 
can be extracted by chemical processes from them. Or, on 
the other hand, we can cause large quantities of elementary 
molecules of difiEerent kinds to combine together to form 
large quantities of molecules of a chemical compound ; and 

^ "Introduction to the Study of Chemical Philosophy," 1 876, p. 4. 



O OPEN-AIR STUDIES 

in either case, by weighing the quantity of each substance 
dealt with, we can find out in what proportions the elements 
are combined in any particular compound. 

We may now glance backwards, and define an atom as the 
smallest quantity of an element that can be driven out of or 
caused to enter into a molecule of a compound in the subtle 
process of destroying or producing any of the known chemical 
combinations of that element. Here we have got down as 
far as we can go in the chemical constitution of a mineral. 
Minerals are made of chemical substances, which are made 
of molecules ; these molecules consist of atoms either (a) of 
different kinds, in which case we are dealing with a com- 
pound, or (b) of only one kind, in which case our substance 
18 an element. 

Now we may try to arrive at a definition of a mineral. 
Let us look at those which we have separated from the 
granite— three materials evidently requiring distinct names, 
evidently differing markedly in their physical characters. 

The clear little lumps are called Quxirtz, and do not tell us 
very much by their external appearance. They break across 
with irregular curving fractures, much as glass does ; and 
they have in this case no regular shape. But they are trans- 
parent, and also very hard; for we cannot scratch them 
With a knife, and they, on the other hand, will scratch glass. 
Moreover, they will not soften and melt, as glass does, when 
held with a pair of forceps in the flame of a Bunsen burner 
■ ^the gas-burner used in chemical laboratories or in ordinary 
tftts-stoves. Clearly, they are not grains of glass. 

If we give them to a chemist, he will find in them the two 
©iements, Silicon and Oxygen, always in the proportion of one 
^tom of silicon to two atoms of oxygen. Quartz is made, in 
^^fc» of the oxide of silicon, commonly called Silica. We may 
i f u^^^ of these grains from granite rocks found anywhere 
^ the world, and yet their chemical composition will be the 
*ftme. 

(y^Aj ^"^^ white or pink bodies are called Orthoclase, or 

th ^ ^^^ Felspar ; these, as we have already noticed, have 
property of breaking across regularly in certain direc- 
""^^ two directions, at any rate — ^when struck with a 
J*** This shows that their internal structure, the way 
^n the molecules are grouped together, differs from 
quartz. Moreover, we can see something of their 




THE MATERIALS OF THE EARTH 7 

external shape; it is often regular, and, even on roughly 
broken surfaces of the rock, the larger orthoclases are seen 
to approach the form of small flat bricks. Then, in turning 
about the rock-specimen in the hand, some of these ortho- 
clases seem to be built up of two parts ; that is, one half of 
the orthoclase catches the light and gives a bright reflection, 
while the other half looks dull ; clearly the planes of fracture 
are differently sloped in the two parts of the mineral, and it 
has not a perfectly simple intemij stractare. 

A good knife will just scratch the orthoclase, if drawn 
firmly across it ; but orthoclase will scratch ordinary glass ; 
we thus learn that it is harder than glass, but not so hard as 
quartz. A little splinter of orthoclase can just be melted 
after holding it for some time in the flame of a Bunsen 
gas-burner. 

Our chemist tells us that this mineral is more complex 
than quartz. He finds in it Silicon, Oxygen, Aluminium, 
Potassium, and generally Sodium. The proportion of these 
elements to one another is always the same, except in the 
case of the two last named. Sometimes there is only potas- 
sium present, and no sodium ; sometimes sodium occurs, and 
then there is less potassium. We say that the potassium may 
be replaced in part by sodium without the principal charac- 
teristics of the mineral being altered. In such cases it must 
be a matter of general consent and judgment as to whether 
we are to call the mineral by a new name when such a re- 
placement occurs. The atoms of sodium are lighter than 
those of potassium ; but any difference in the weight of a 
given bulk of orthoclase, according as it contains potassium, 
or both potassium and sodium, would be very trifling. Cases 
often occur, moreover, where a lighter element replaces a 
heavier one, and yet the resulting variety of the mineral is 
actually heavier than the ordinary form. The molecules con- 
taining the lighter element must in such cases lie closer 
together, i.e., there must be more of them in a given space, 
than occurs when only molecules containing the heavier 
element are present. 

So we may note that the chemical composition of some 
minerals may vary slightly, varieties being set up which are 
grouped together under the common mineral name. A mole- 
cule of our typical orthoclase contains 2 atoms of potassium, 
2 of aluminium, 6 of silicon, and i6 of oxygen. But in most 



8 OPEN-AIR STUDIES 

specimens of orthoclase there are some molecules in which 
two atoms of sodium take the place of the two atoms of potas- 
sium. When such molecules are shown by a chemical analysis 
to be numerous, we call the mineral variety Soda-Orthoclase. 

Our third mineral in the granite is called Mica — the plate- 
like substance which is easily dug out with the knife, and 
which gives such a shining appearance to many specimens of 
the rock. Some micas are pale and silvery ; others are quite 
dark, being bronze-coloured or black ; but they have many 
characters in common. Again and again their proper form 
can be seen ; their molecules are clearly capable of building 
up six-sided plates. This structure is so common that it can- 
not be accidental ; and careful measures show that the angles 
of the hexagonal figure are kept the same in the same chemical 
variety. Such a structure is called a crystal ; and a little 
observation will show us that the orthoclase also is in the 
form of crystals, though they have probably not been able to 
grow to such perfection. The mica splits very easily in one 
direction, so that we can flake off thin flexible plates ; and 
even the blacker micas are no longer opaque when one of their 
thin plates is held up to the light. The mineral is quite soft, 
and can often be scratched by the thumb-nail. 

The chemical composition of the micas is still more 
complex than that of the orthoclase felspar, but all common 
varieties contain Silicon, Oxygen, Aluminium, Potassium, 
Magnesium, Iron, and Hydrogen. The pale varieties con- 
tain little iron and usually little magnesium ; the dark 
varieties are richer in these elements and poorer in silicon 
and aluminium. There may be a good deal of replacement 
of one element by another in the mica series, the general 
external characters being retained ; and several different 
kinds or species of mica are recognised, and are known by 
distinct mineral names. 

If we are so fortunate as to find a granite with a number 
of small hollows in it, perhaps half-an-inch or an inch across, 
such as occur in the famous rocks of the northern part of 
the Mourne Mountains, then we may see that all the 
minerals which we have discussed are capable of forming 
crystals, wherever freedom is given to them and when they 
are not too much squeezed together. In such hollows we 
find the mica, and the orthoclase, and the quartz itself, 
delicately crystallised, beautifully and regularly shaped, so 



THE MATERIALS OF THE EARTH 9 

that persons looking at the handsome crystals in public 
collections often think that they have been artificially cut 
and polished. But you have only to go into the hills, and 
search in cracks and hollows for yourselves, to find that 
crystals occur naturally, and that they are, indeed, the form 
frequently adopted by natural chemical substances. And, 
further, the crystals of one compound usually differ from 
those of another ; the sides make different angles one with 
another, even if the forms are very much alike; so that, 
by careful observation and measurement of the angles in 
various crystals, we can use the outer shape to help us in 
determining the nature of the mineral. 

And now we can at last arrive at our definition. A 

mineral is a natural substance, formed without the action of 

plants or animals. Its chemical composition is constant, or 

vai^ies only by a well-defined series of chemical replacements. 

Under favourable conditions, it assumes a ci-ystalline form. 

One mineral is known from another by a number of 
characters which must be considered all together; and 
these will be found stated in any text-book of mineralogy.^ 
Let us run over the most important of these characters 
here. 

I. Colour. — ^When there are several minerals in a rock, 
this character often clearly marks out one from another. 
But it is of far less importance than might be supposed, 
since many common minerals are coloured by some trifling 
impurity; a sort of stain runs through them, as it were, 
and in their pure condition they are colourless. Metallic 
ores, however, usually have characteristic colours ; thus Iron 
Pyrites, the common iron sulphide, is brass-yellow, and 
Native Copper, the natural element, is copper-red. But, on 
the other hand, the red gem Kuby and the blue Sapphire are 
mere varieties of the same mineral species, Corundum, the 
composition of both being aluminium oxide coloured by a 
substance very insignificant in amount.^ Hence we must 

^ Such as Hatch, "Mineralogy" (Whittaker & CJo.) ; Rutley, "Mineralogy" 
(T. Murby). 

^ Artificial corundum has been coloured red (ruby) by adding chromium 
fluoride to the materials employed ; and, curiously enough, the addition of 
this same substance in varying proportions has given rise to sapphires and to 
a green variety. Rubies have also been made by adding potassium bichro- 
mate, and sapphires by adding cobalt oxide (Fouqud and L^vy, Synthase 
des Mindraux et des Roches, pp. 220 and 222). 



8 OPEN-AIR STUDIES 

specimens of orthoclase there are some molecules in which 
two atoms of sodium take the place of the two atoms of potas- 
sium. When such molecules are shown by a chemical analysis 
to be numerous, we call the mineral variety Soda-Orthoclase. 

Our third mineral in the granite is called Mica — the plate- 
like substance which is easily dug out with the knife, and 
which gives such a shining appearance to many specimens of 
the rock. Some micas are pale and silvery ; others are quite 
dark, being bronze-coloured or black ; but they have many 
characters in common. Again and again their proper form 
can be seen ; their molecules are clearly capable of building 
up six-sided plates. This structure is so common that it can- 
not be accidental ; and careful measures show that the angles 
of the hexagonal figure are kept the same in the same chemical 
variety. Such a structure is called a crystal ; and a little 
observation will show us that the orthoclase also is in the 
form of crystals, though they have probably not been able to 
grow to such perfection. The mica splits very easily in one 
direction, so that we can flake off thin flexible plates ; and 
even the blacker micas are no longer opaque when one of their 
thin plates is held up to the light. The mineral is quite soft, 
and can often be scratched by the thumb-nail. 

The chemical composition of the micas is still more 
complex than that of the orthoclase felspar, but all common 
varieties contain Silicon, Oxygen, Aluminium, Potassium, 
Magnesium, Iron, and Hydrogen. The pale varieties con- 
tain little iron and usually little magnesium ; the dark 
varieties are richer in these elements and poorer in silicon 
and aluminium. There may be a good deal of replacement 
of one element by another in the mica series, the general 
external characters being retained ; and several different 
kinds or species of mica are recognised, and are known by 
distinct mineral names. 

If we are so fortunate as to find a granite with a number 
of small hollows in it, perhaps half-an-inch or an inch across, 
such as occur in the famous rocks of the northern part of 
the Mourne Mountains, then we may see that all the 
minerals which we have discussed are capable of forming 
crystals, wherever freedom is given to them and when they 
are not too much squeezed together. In such hollows we 
find the mica, and the orthoclase, and the quartz itself 
delicately crystallised, beautifully and regularly Bhi^e%:; ^ 




8 OPEN-AIR STUDIES 

specimens of orthoclase there are some molecules in which 
two atoms of sodium take the place of the two atoms of potas- 
sium. When such molecules are shown by a chemical analysis 
to be numerous, we call the mineral variety Soda-Orthoclase. 

Our third mineral in the granite is called Mica — the plate- 
like substance which is easily dug out with the knife, and 
which gives such a shining appearance to many specimens of 
the rock. Some micas are pale and silvery ; others are quite 
dark, being bronze-coloured or black ; but they have many 
characters in common. Again and again their proper form 
can be seen ; their molecules are clearly capable of building 
up six-sided plates. This structure is so common that it can- 
not be accidental ; and careful measures show that the angles 
of the hexagonal figure are kept the same in the same chemical 
variety. Such a structure is called a crystal ; and a little 
observation will show us that the orthoclase also is in the 
form of crystals, though they have probably not been able to 
grow to such perfection. The mica splits very easily in one 
direction, so that we can flake off thin flexible plates ; and 
even the blacker micas are no longer opaque when one of their 
thin plates is held up to the light. The mineral is quite soft, 
and can often be scratched by the thumb-nail. 

The chemical composition of the micas is still more 
complex than that of the orthoclase felspar, but all common 
varieties contain Silicon, Oxygen, Aluminium, Potassium, 
Magnesium, Iron, and Hydrogen. The pale varieties con- 
tain little iron and usually little magnesium ; the dark 
varieties are richer in these elements and poorer in silicon 
and aluminium. There may be a good deal of replacement 
of one element by another in the mica series, the general 
external characters being retained ; and several different 
kinds or species of mica are recognised, and are known by 
distinct mineral names. 

If we are so fortunate as to find a granite with a number 
of small hollows in it, perhaps half-an-inch or an inch across, 
such as occur in the famous rocks of the northern part of 
the Mourne Mountains, then we may see that all the 
minerals which we have discussed are capable of forming 
crystals, wherever freedom is given to them and when they 
are not too much squeezed together. In such hollows we 
find the mica, and the orthoclase, and the quartz itself, 
delicately crystallised, beautifully and regularly shaped, so 



THE MATERIALS OF THE EARTH 9 

that persons looking at the handsome crystals in public 
collections often think that they have been artificiaUy cut 
and polished. But you have only to go into the hills, and 
search in cracks and hollows for yourselves, to find that 
crystals occur naturally, and that they are, indeed, the form 
frequently adopted by natural chemical substances. And, 
further, the crystals of one compound usually diiler from 
those of another ; the sides make different angles one with 
another, even if the forms are very much alike; so that, 
by careful observation and measurement of the angles in 
various crystals, we can use the outer shape to help us in 
detennining the nature of the mineral. 

And now we can at last arrive at our definition. A 

Tnineral is a natural substance^ formed without the action of 

plants or animals. Its chemical composition is constant, or 

vai'ies only by a well-defined series of chxmical replacements. 

Under favourable conditions, it assumes a ciystalline form. 

One mineral is known from another by a number of 
characters which must be considered all together; and 
these will be found stated in any text-book of mineralogy.^ 
Let us run over the most important of these characters 
here. 

I. Colour. — When there are several minerals in a rock, 
this character often clearly marks out one from another. 
But it is of far less importance than might be supposed, 
since many common minerals are coloured by some trifling 
impurity; a sort of stain runs through them, as it were, 
and in their pure condition they are colourless. Metallic 
ores, however, usually have characteristic colours ; thus Iron 
Pyrites, the common iron sulphide, is brass-yellow, and 
Native Copper, the natural element, is copper-red. But, on 
the other hand, the red gem Kuby and the blue Sapphire are 
mere varieties of the same mineral species. Corundum, the 
composition of both being aluminium oxide coloured by a 
substance very insignificant in amount.^ Hence we must 

^ Such as Hatch, "Mineralogy" (Whittaker & Co.) ; Rutley, "Mineralogy" 
(T. Murby). 

'^ Artificial corundum has been coloured red (ruby) by adding chromium 
fluoride to the materials employed ; and, curiously enough, the addition of 
this same substance in varying proportions has given rise to sapphires and to 
a green variety. Rubies have also been made by adding potassium bichro- 
mate, and sapphires by adding cobalt oxide (Fouqud and Ldvy, Synthase 
des MirUraux et des Roches, pp. 220 and 222). 



« • 



OPEN-AIR STUDIES 



• - .. 



Ii\' earfy times, it was most important that man should 
find but how to make things. He had to build shelters 
agaTrisfc'the rain; he had to find weapons with which to 
coiilb4t the wild beasts ; he had to carve out gourds into 
Yes^s in which liquids could be carried. But all these 
.thin'gs were by no means easy, and required a good deal of 
•.ol^ervation. Nature was already doing many wonderful 
r'Vtfdngs in the great world round about, and it was well to 
-••.. Vatch, and even to imitate, these closely. After all, what- 
'••• ever was required by man had to be made out of natural 
materials. One result of this struggle with diflSculties was 
that early man took to studying the stones beneath his feet. 
Some of his earliest instruments were made of stone ; and 
we know that many savage tribes have only given up the 
use of stone axes and stone arrow-heads since the arrival of 
European traders on their coasts. Primitive peoples would 
soon observe that some kinds of stone break more easily 
than others, that some kinds can be chipped in almost any 
direction so as to give a sharp cutting edge, and that some, 
again, are far superior in hardness or durability to the 
rest. It became important to search among the rocks for 
materials suited to each special purpose ; and thus began, 
perhaps, the first researches into the structure of the world 
around us. 

When native metals were discovered, and when, moreover, 
it was found that valuable substances could be extracted by 
heat from stones utterly unlike them in appearance, the 
study of the earth became a much more complicated matter ; 
and at last a few thoughtful persons took to inquiring how 
such-and-such materials, used by man in the manufacture of 
common things, came themselves to be made in the heart of 
the old solid earth. Then began the science of Qeology, the 
systematic study of the way in which the world is built up, 
and of the natural changes which go on within it and upon it. 
Even the earliest men must have seen that the earth 
changed around them. Floods came down, and covered 
smiling landscapes with sand and stones from distant hills ; 
volcanoes broke out, and heaped ashes and lava upon the 
surface ;: the sea worked against the land, and washed the 
coast steadily away ; while in other places tawny rivers wan- 
dered through the plains and thrust their burden of mud in 
long banks far to seaward. 



THE MATERIALS OF THE EARTH 3 

Thus the earth changed its surface, growing at one 
place, decaying away at another ; and men began to realise 
that it had a lustory, beside which their own lives were short 
indeed. And yet it is only in the last hundred years or so 
that we have been able to read this history at all clearly, 
and even now we understand only that end of it which lies 
nearest to ourselves. 

Before we go out and try to read a page or two of this 
history, we must learn something of the materials with 
which we have to deal. Of what, then, is the earth actually 
made? 

As a matter of fact, we know only a very small part of 
the vast globe on which we live. The centre of the earth 
lies 40CX) miles beneath us, and our mines and borings pene- 
trate the great mass to a depth of only about a mile. But, 
as we shall see later, the outer layers of the earth have 
become wrinkled and folded, so that rocks which once lay 
far below the surface have been brought up within our 
reach. Hence in some places, immediately under the loose 
soil, we may find materials which were formerly ten or 
fifteen miles lower down; and this enables us to say that 
we have some idea of the constitution of the globe to a 
depth of fifteen miles from the surface. It is not much, 
this mere outer shell, fifteen miles thick all round the 
earth; but it is all we shall have to deal with, and we 
speak of this accessible region as the crust of the earth. 

This solid crust is made of rocks. Any workman in a 
quarry will tell us, for instance, that granite is a rock, or 
that sandstone is a rock. But, when we examine these two 
materials, we see that they are made up of distinct particles 
which themselves are worth inquiring into. The granite 
has clear little lumps, like glass, in it ; and dull white or 
pink bodies, which seem to break across in a regular manner, 
with smooth or step- like surfaces ; and soft flaky things 
which reflect the light brilliantly, and which can be pulled 
away, or dug out with a knife, in the form of little shining 
plates. The sandstone, on the other hand, is made of 
practically one kind of material throughout, in the form of 
a number of hard and somewhat rounded grains. 

In each case we call these constituents, having characters 
of their own, the minerals which compose the rock. The 
granite consists of at least three distinct minerals, the sand- 



4 OPEN-AIR STUDIES 

stone of only one. Now, if we break up a rock, and select 
a number of fragments of any one kind of mineral, a chemist 
will show us that this mineral is itself made up of certain 
chemical substances, which he can separate and accurately 
determine. He will be able to find out in what proportions 
these chemical substances are present, and will thus give us 
an account of the chemical constitution of the mineral. 

But what about these various substances? They may 
be stated by our friendly chemist to be chemical compounds, 
and these can be further split up into their elements. Or, to 
take the simplest case, our mineral may possibly consist of 
merely one element. 

Here we may remind ourselves of some of our chemical 
notions. We must go back, indeed, to the foundations of 
several sciences for the correct understanding of our rocks, 
and this first chapter is going to be a serious one, before we 
can fairly get out into the country and the open air. But 
we must remember that all the things with which we shall 
deal are quite natural, all come from the earth itself that 
stretches round us ; and those parts of chemistry and physics 
which are possibly a little dull to us seem so merely because 
we cannot handle or directly observe the things about which 
we are being told. If we could see the tiny ** atoms " 
moving in the " molecule " of a substance, we should pro- 
bably be as delighted and as fascinated as if we were sitting 
on a monntain-peak and watching the great balance of the 
stars. 

A chemical element is a substance that cannot be split 
up, by any means at present in our power, into any other 
substances with diJBferent properties from those by which it 
is itself characterised. It is thus the simplest kind of 
material known to us. Gold, silver, copper, and iron are 
elements; sulphur is an element; so also is carbon, well 
known to us in its commonest form, the " black-lead " of 
our pencils. There are now about seventy elements known, 
and others, at present doubtful, are likely to be added to 
the Ust 

The ancients regarded the earth as an element in itself, 
something existing as a foundation for other things, the 
remaining elements being air, fire, and water. What we 
now know as elements were often treated in earlier times 
as varied forms of the same fundamental material ; but all 



THE MATERIALS OF THE EARTH 5 

experiment has shown us up to the present that there are 
really, in this earth and throughout the mighty universe, a 
number of difiEerent kinds of matter. To be quite simple in 
our conceptions, we might wish to say that all elements are 
made up of difiEerent arrangements of particles of one first- 
formed matter ; but that would be merely guess-work, and 
at present we cannot get beyond our seventy elements. 

If we conceive the smallest particle of an element that 
can independently exist, we may call such a particle an 
cUom, It will have a certain weight, and the atoms of 
difiEerent elements difiEer in their weights. But any quantity 
of matter that we can see, even with a microscope, must 
consist of enormous numbers of atoms. 

The atoms are said to be grouped together in molecules, 
or ** little masses." Chemists regard the molecule of certain 
elements as consisting of only one atom ; in others, two or 
even six atoms may form the molecule. A molecule has 
been defined by Professor Tilden as " the smallest quantity 
which is able to take part in or result from a chemical 
change." ^ 

A chemical compound is built up of molecules, each of 
which consists of atoms of more than one kind. In the 
simplest compounds the molecule consists of only two 
atoms, one atom of one element being combined with one 
of another. The elements have been shown to combine 
together in fixed proportions, forming compounds with dis- 
tinctive properties. We may hence say that the molecule 
of a compound is the smallest particle into which the sub- 
stance could be divided while yet retaining its peculiar 
chemical constitution. Further splitting might give us cer- 
tain simpler compounds; but ultimately the actual atoms, 
or groups of similar atoms, of each molecule would be set 
free ; in other words, the compound would separate into 
its elements. 

All this may seem beyond human observation ; but large 
quantities of molecules of a compound can be dealt with in 
our experiments, and large quantities of elementary molecules 
can be extracted by chemical processes from them. Or, on 
the other hand, we can cause large quantities of elementary 
molecules of difiEerent kinds to combine together to form 
large quantities of molecules of a chemical compound ; and 

^ "Introduction to the Study of Chemical Philosophy," 1876, p. 4. 



LIST OF ILLUSTRATIONS 



FULL-PAGE ILLUSTRATIONS 



GwM-GLAS, Pass of Llanbbbis 



PLATB 

I. Waterfall forming an Alcove in Stratified Bocks, 

Glencar, Go. Sligo 

II. Snow-filled Cirque at the base of the Matterhom, 
Switzerland 

III. Stratified Sands and Gravels, Antrim 

IV. The Sea breaking on a rocky coast, near Bally- 

castle, Co. Antrim 

V. The Crater-rim of the Pay de Pariou, Auvergne . 
YI. Columns at the Giant's Causeway, Co. Antrim, in 

Basaltic Lava-flow . . ... 
VIL Dyke of Dolerite, Quarry on Cave Hill, Belfast 
YIII. Columnar and massive Lava-flows at Fleaskin Head, 

Co. Antrim 

IX. Granite exposed on slope above the Eilkeel Biver, 

Mourne Mountains, Co. Down .... 

X. Fossil Shells in Pliocene Sands, Felixstowe, Suffolk . 

XI. Contorted Upper Jurassic Strata, Stare Cove, Lul- 

worth, Dorsetshire 



PronHtpiece 



To face page 42 



56 
76 

96 
150 

172 
181 

183 

190 
220 



f> 



284 



ILLUSTRATIONS IN TEXT 



FIO. 



1. Pot-hole, Glenariff, Co. Antrim 

2. Section illustrating the origin of Springs 

3. Section showing principle of Artesian Springs and Wells, and 

origin of Bournes 

4. Section of Gorge choked with Alluvium 

5. Section showing a slope of i in 17 

xi 



PAGE 

59 



60 

75 
79 



LIST OF ILLUSTBATIONB I 

pbtions of Aipioe valley and Scotcb glens . 
d Lake-TeiTBCes of the Salt- Lake area of Utah 
e island of Voloano in eraption 
Pmall Conea thrown up on Etna .... 

n of a Volcano 

mating Bcoria above the Snbmariiie Bmption oft 

iHicTOBCOpic section of Obsidian 

I Microscopic BOctlon of Basalt 

[ The Fay <le Lassolas and the Pu? de la Vacbe 

;. Oeologioal Hap, Bhonicg Lava-flows descending from I 

Auve^ne 

H6. Qranite Piimacles, Monme Hoantaiue .... 
K7. Unconformable Junction, with Overlap and Overstep . 
I. Internal cast of a Ceritbiiim, Portland Stone 

I. a. Pecttn Beaveri ; b. Peetea dnctia; c, Pectta Ulanditnii 

} to. TrilobitcB 

. Section across the Surrey Hills > 

' ax. Section illnstrating Variation of Width of Outcrop 
23. Sand with Spicules of Siliceous Sponges, Hythe Beds, Saiiej 
34. intyloetraa ffigat 

25. Acanthocerai rotluitaageiue ..... 

26. AeUnoeamax pUnat < - 

27. Inoeeramut Cuvieri 

zS. Section illustrating Fan-Strnctnre in a Uoautain-Cbain 

29. Section Ulnstiating Recumbent Folds 

30. Section across a Fault 

31. Plan of a Fault in inclined Strata 

31. Kidges and Valleys formed by Folds in the Jara Uountains 
33. Beoombeot Synclinal and Folding on the Win^ille 



or THK KAllTH 3 

"is surfac(\ growing «it one 

• : and ni(Mi began to realist* 

•Ii their own lives were short 

he* hist hundred years or so 

i this history at all clearly, 

Iv that end of it which lit»s 

t*ad a page or two of this 
■g of the materials with 
rlien, is the earth actually 

: »idy a very small ])art of 

The centre of the earth 

mines and borings pene- 

nlv about a mile. J>ut, 

.t»rs of tin* earth have 

• rocks which onct* lay 

"ought u]) within our 

liat(*ly under the loos(» 

vere fornKM'lv t(*n or 

•labh^s us to say that 

•n of the globe to a 

■I'. It is not much, 

hick all round the 

deal with, and we 

ist of the earth. 

Any workman in a 

•anitc* is a rock, or 

• 'xamine these two 

f distinct ])articles 

:to. 1'he granit(» 

nd dull white or 

I regular m/inner, 

oft llaky things 

!i can be ])ulled 

•f little shining 

m1. is made of 

in th(» form of 

ins. 

• ing characters 

h(* rock, ^riit* 

als, the sand- 



LIST or ILLUSTRATIONS 



FULL-PAGE ILLUSTRATIONS 



GwM-OLAS, Pass of Llanbbbis 

PLATB 

I. Waterfall forming an Alcove in Stratified Bocks, 

Glencar, Go. Sligo 

II. Snow-filled Girqne at the base of the Matterhom, 
Switzerland 

III. Stratified Sands and Gravels, Antrim 

IV. The Sea breaking on a rocky coast, near Bally- 

castle, Go. Antrim 

V. The Grater-rim of the Puy de Fariou, Auvergne . 
yi. Golnmns at the Giant's Gauseway, Go. Antrim, in 

Basaltic Lava-flow . . . . 
VIL Dyke of Dolerite, Quarry on Gave Hill, Belfast 
VIII. Golnmnar and massive Lava-flows at Fleaskin Head, 

Go. Antrim 

IX. Granite exposed on slope above the Eilkeel River, 

Mourne Mountains, Go. Down .... 

X. Fossil Shells in Pliocene Sands, Felixstowe, Suffolk . 

XI. Gontorted Upper Jurassic Strata, Stare Gove, Lul- 

worth, Dorsetshire 



PronHtpiece 



To face page 42 



56 
76 

96 
150 

172 

181 

183 

190 
220 



)> 



284 



ILLUSTRATIONS IN TEXT 

FIO. PAGE 

1. Pot-hole, Glenariff, Go. Antrim 31 

2. Section illustrating the origin of Springs 59 

3. Section showing principle of Artesian Springs and Wells, and 

origin of Bournes 60 

4. Section of Gorge choked with Alluvium 75 

5. Section showing a slope of i in 17 *l<^ 

xi 



/ 



LIST OF ILLUSTEATIONS 



FULL-PAGE ILLUSTRATIONS 



GwM-GLAS, Pass of Llanbbbis 



PLATE 

I. Waterfall forming an Alcove in Stratified Bocks, 

Glencar, Co. Sligo 

II. Snow-filled Girqne at the base of the Matterhom, 
Switzerland 

III. Stratified Sands and Gravels, Antrim 

IV. The Sea breaking on a rocky coast, near Bally- 

castle, Co. Antrim 

V. The Crater-rim of the Pay de Pariou, Auvergne . 
VI. Columns at the Giant's Causeway, Co. Antrim, in 

Basaltic Lava-flow . . . . 
YIL Dyke of Dolerite, Quarry on Cave Hill, Belfast 
VIII. Columnar and massive Lava-flows at Fleaskin Head, 

Co. Antrim 

IX. Granite exposed on slope above the Eilkeel River, 

Mourne Mountains, Co. Down .... 

X. Fossil Shells in Pliocene Sands, Felixstowe, Suffolk . 

XI. Contorted Upper Jurassic Strata, Stare Cove, Lul- 

worth, Dorsetshire 



PronHtpiece 



To face page 42 



56 
76 

96 
150 

172 
181 

183 

190 
220 



tf 



284 



ILLUSTRATIONS IN TEXT 

FIG. PAGE 

1. Pot-hole, Glenariff, Co. Antrim 31 

2. Section illustrating the origin of Springs 59 

3. Section showing principle of Artesian Springs and Wells, and 

origin of Bournes 60 

4. Section of Gorge choked with Alluvium 75 

5. Section showing a slope of i in 17 *l<^ 

xi 



XU LIST OF ILLUSTRATIONS 

FIG. PAQB 

6. Sections of Alpine valley and Scotch glens 83 

7. Old Lake-Terraces of the Salt-Lake area of Utah . . • 139 

8. The island of Volcano in eruption 155 

9. Small Cones thrown up on Etna 159 

la Section of a Volcano 161 

1 1. Floating Scorias above the Submarine Eruption off Fantelleria . 163 

12. Microscopic section of Obsidian 165 

13. Microscopic section of Basalt 167 

14. The Puy de Lassolas and the Fuy de la Vache . .176 

15. Geological Map, showing Lava-flows descending from Fuys in 

Auvergne 177 

16. Granite Pinnacles, Mourne Mountains 193 

17. Unconformable Junction, with Overlap and Overstep . .219 

18. Internal cast of a Cerithium, Portland Stone .... 221 

19. a, Pecten Beaveri ; b. Peeten einctus ; c, Pecten idandieus . 225 

20. Trilobites 235 

21. Section across the Surrey Hills 249 

22. Section illustrating Variation of Width of Outcrop . 253 

23. Sand with Spicules of Siliceous Sponges, Hythe Beds, Surrey . 261 

24. Aneyloeeras gigas 269 

25* Acanthoeeras rothomagense 271 

26. Aetiiiocamax plenus 273 

27. Inoeeramits Cuvieri 274 

28. Section illustrating Fan-Structure in a Mountain-Chain 284 

29. Section illustrating Recumbent Folds 284 

3a Section across a Fault 285 

31. Plan of a Fault in inclined Strata 286 

32. Ridges and Valleys formed by Folds in the Jura Mountains . 291 

33. Recumbent Synclinal and Folding on the Windgalle . . 297 



OPEN-AIE STUDIES 



CHAPTER I 

THE MATERIALS OF THE EARTH 

When we were children, as soon as we could think and 
ask questions, most of us tried to find out two important 
matters — how to make things, and what things are made of. 
The little boy who cut open his drum to see where the sound 
came from was not so entirely foolish as is sometimes repre- 
sented, for he at least made an interesting and valuable 
experiment. He learnt in this way that a drum was best 
constructed by stretching two thin skins opposite to one 
another, and shutting in a quantity of air between them. 
He was not satisfied with the mere showy outsides of things, 
or with the royal arms of Great Britain and Ireland painted 
on the wooden barrel of the drum. He felt that the sound', 
which was the great feature of the instrument, must have a 
cause ; and he set to work to find out something about it for 
himself. Probably he only got as far as seeing how the 
drum was made, and had to ask his father for the reason of 
this particular arrangement. But that is what every one has 
to do, and why no great discovery is likely to be of use to 
us unless we know what other people have previously dis- 
covered. In the same way, we cannot write a passably useful 
book unless we are near the 50,000 volumes of a well-stocked 
public library. Our knowledge in this world does not go on 
by jumps and bounds, but by a study of what others have 
seen and done, and of the records of their failure or success. 
Even if, after a long series of experiments, we have to leave 
our old drums damaged and cut open, we may soon have wit 
enough to make newer and better ones for the service of 
ourselves and our descendants. 






OPEN-AIR STUDIES 



In* e&rfy times, it was most important that man shonld 
find but how to make things. He had to build shelters 
agams^'the rain; he had to find weapons with which to 
cqiilb^t the wild beasts ; he had to carve out gourds into 
vesfeiftls in which liquids could be carried. But all these 
.thln'gs were by no means easy, and required a good deal of 
•.ol^ervation. Nature was already doing many wonderful 
\:iidng& in the great world round about, and it was well to 
•, Vatch, and even to imitate, these closely. After all, what- 
• • ever was required by man had to be made out of natural 
materials. One result of this struggle with diflSculties was 
that early man took to studying the stones beneath his feet. 
Some of his earliest instruments were made of stone ; and 
we know that many savage tribes have only given up the 
use of stone axes and stone arrow-heads since the arrival of 
European traders on their coasts. Primitive peoples would 
soon observe that some kinds of stone break more easily 
than others, that some kinds can be chipped in almost any 
direction so as to give a sharp cutting edge, and that some, 
again, are far superior in hardness or durability to the 
rest. It became important to search among the rocks for 
materials suited to each special purpose ; and thus began, 
perhaps, the first researches into the structure of the world 
around u& 

When native metals were discovered, and when, moreover, 
it was found that valuable substances could be extracted by 
heat from stones utterly unlike them in appearance, the 
study of the earth became a much more complicated matter ; 
and at last a few thoughtful persons took to inquiring how 
such-and-such materials, used by man in the manufacture of 
common things, came themselves to be made in the heart of 
the old solid earth. Then began the science of Gteology, the 
systematic study of the way in which the world is built up, 
and of the natural changes which go on within it and upon it. 
Even the earliest men must have seen that the earth 
changed around them. Floods came down, and covered 
smiling landscapes with sand and stones from distant hills ; 
volcanoes broke out, and heaped ashes and lava upon the 
surface ;; the sea worked against the land, and washed the 
coast steadily away ; while in other places tawny rivers wan- 
dered through the plains and thrust their burden of mud in 
long banks far to seaward. 



THE MATERIALS OF THE EARTH 3 

Thus the earth changed its surface, growing at one 
place, decaying away at another ; and men began to realise 
that it had a history, beside which their own lives were short 
indeed. And yet it is only in the last hundred years or so 
that we have been able to read this history at all clearly, 
and even now we understand only that end of it which lies 
nearest to ourselves. 

Before we go out and try to read a page or two of this 
history, we must learn something of the materials with 
which we have to deal. Of what, then, is the earth actually 
made? 

As a matter of fact, we know only a very small part of 
the vast globe on which we live. The centre of the earth 
lies 4CXX) miles beneath us, and our mines and borings pene- 
trate the great mass to a depth of only about a mile. But, 
as we shall see later, the outer layers of the earth have 
become wrinkled and folded, so that rocks which once lay 
far below the surface have been brought up within our 
reach. Hence in some places, immediately under the loose 
soil, we may find materials which were formerly ten or 
fifteen miles lower down; and this enables us to say that 
we have some idea of the constitution of the globe to a 
depth of fifteen miles from the surface. It is not much, 
this mere outer shell, fifteen miles thick all round the 
earth; but it is all we shall have to deal with, and we 
speak of this accessible region as the crust of the earth. 

This solid crust is made of rocks. Any workman in a 
quarry will tell us, for instance, that granite is a rock, or 
that sandstone is a rock. But, when we examine these two 
materials, we see that they are made up of distinct particles 
which themselves are worth inquiring into. The granite 
has clear little lumps, like glass, in it ; and dull white or 
pink bodies, which seem to break across in a regular manner, 
with smooth or step- like surfaces ; and soft flaky things 
which reflect the light brilliantly, and which can be pulled 
away, or dug out with a knife, in the form of little shining 
plates. The sandstone, on the other hand, is made of 
practically one kind of material throughout, in the form of 
a number of hard and somewhat rounded grains. 

In each case we call these constituents, having characters 
of their own, the minerals which compose the rock. The 
granite consists of at least three distinct minerals, the sand- 



2 _. OPKN-AIR STUDIES 

ln-et/rij times, it was most important that man ehonld 
find bn'C how to make things, lie had to build aheltera 
agaiHBl'the rain; he had to find weapons with which to 
coiilh^t the wild beasts ; he had to carve out gourde into 
VOsMls in which liquids could be carried. But all these 
.thlii^ were by no means easy, and reqnired a good deal of 
■'.oIiBervation. Nature was already doing many wonderful 
.'.-(iiiiigB in the great world round about, and it was well to 
.'watch, and even to imitate, these closely. After all, whut- 
" ever was reqnired by man had to be made out of natural 
materials. One reanlt of this struggle with difficulties was 
that early man took to etudying the stones beneath his feet. 
Some of his earliest instruments were made of stone ; and 
we know that many savage tribes have only given wp the 
nee of stone axes and stone arrow-heads since the arrival o£ 
European traders on their coasts. Primitive peoples would 
soon observe that some kinds of stone break more easily 
than others, that some kinds can be chipped in almost any 
direction so as to give a sharp cutting edge, and that some, 
again, are far euperior in hardness or durability to the 
rest. It became important to search among the rooks for 
materials suited to each special purpose ; and thus began, 
perhaps, the first researches into the structure o£ the world 
around n& 

When native metals were discovered, and when, moreover, 
it was found that valuable substances could be extracted by 
heat from stones utterly unlike them in appearance, the 
study of the earth became a much more complicated matter ; 
and at last a few thoughtful persons took to inquiring how 
such-and-such materials, used by man in the manufacture of 
common things, came themselves to be made in the heart of j 
the old solid earth. Then began the science of Geology, tl 
systematic study of the way in which the world is boilt i 
and of the natural changes which go on within it and q 

Even the earliest men must have seen that 1' 
changed around them. Floods came down, i 
smiling landscapes with sand and stones £ 
volcanoes broke out, and heaped ashes i 
surface ; the sea worked against the 1 
coast steadily away ; while in others'"' 
dered through the plair- 
long banks far to seai 





4 OPEN-AIR STUDIES 

stone of only one. Now, if we break up a rock, and select 
a number of fragments of any one kind of mineral, a chemist 
will show us that this mineral is itself made up of certain 
chemical substances, which he can separate and accurately 
determine. He will be able to find out in what proportions 
these chemical substances are present, and will thus give us 
an account of the chemical constitution of the mineral. 

But what about these various substances? They may 
be stated by our friendly chemist to be chemical compounds, 
and these can be further split up into their elements. Or, to 
take the simplest case, our mineral may possibly consist of 
merely one element. 

Here we may remind ourselves of some of our chemical 
notions. We must go back, indeed, to the foundations of 
several sciences for the correct understanding of our rocks, 
and this first chapter is going to be a serious one, before we 
can fairly get out into the country and the open air. But 
we must remember that all the things with which we shall 
deal are quite natural, all come from the earth itself that 
stretches round us ; and those parts of chemistry and physics 
which are possibly a little dull to us seem so merely because 
we cannot handle or directly observe the things about which 
we are being told. If we could see the tiny " atoms " 
moving in the " molecule " of a substance, we should pro- 
bably be as delighted and as fascinated as if we were sitting 
on a mountain-peak and watching the great balance of the 
stars. 

A chemical element is a substance that cannot be split 
up, by any means at present in our power, into any other 
substances with diflFerent properties from those by which it 
is itself characterised. It is thus the simplest kind of 
material known to us. Gold, silver, copper, and iron are 
elements; sulphur is an element; so also is carbon, well 
known to us in its commonest form, the "black-lead" of 
our pencils. There are now about seventy elements known, 
and others, at present doubtful, are likely to be added to 
the list. 

The ancients regarded the earth as an element in itself, 
something existing as a foundation for other things, the 
remaining elements being air, fire, and water. What we 
now know as elements were often treated in earlier times 
as varied forms of the same fundamental material ; but all 



THE MATERIALS OF THE EARTH 5 

experiment has shown us up to the present that there are 
really, in this earth and throughout the mighty universe, a 
number of diflFerent kinds of matter. To be quite simple in 
our conceptions, we might wish to say that all elements are 
made up of diflFerent arrangements of particles of one first- 
formed matter ; but that would be merely guess-work, and 
at present we cannot get beyond our seventy elements. 

If we conceive the smallest particle of an element that 
can independently exist, we may call such a particle an 
atom. It will have a certain weight, and the atoms of 
different elements differ in their weights. But any quantity 
of matter that we can see, even with a microscope, must 
consist of enormous numbers of atoms. 

The atoms are said to be grouped together in molecules, 
or " little masses." Chemists regard the molecule of certain 
elements as consisting of only one atom ; in others, two or 
even six atoms may form the molecule. A molecule has 
been defined by Professor Tilden as " the smallest quantity 
which is able to take part in or result from a chemical 
change." ^ 

A chemical compound is built up of molecules, each of 
which consists of atoms of more than one kind. In the 
simplest compounds the molecule consists of only two 
atoms, one atom of one element being combined with one 
of another. The elements have been shown to combine 
together in fixed proportions, forming compounds with dis- 
tinctive properties. We may hence say that the molecule 
of a compound is the smallest particle into which the sub- 
stance could be divided while yet retaining its peculiar 
chemical constitution. Further splitting might give us cer- 
tain simpler compounds; but ultimately the actual atoms, 
or groups of similar atoms, of each molecule would be set 
free ; in other words, the compound would separate into 
its elements. 

All this may seem beyond human observation ; but large 
quantities of molecules of a compound can be dealt with in 
our experiments, and large quantities of elementary molecules 
can be extracted by chemical processes from them. Or, on 
the other hand, we can cause large quantities of elementary 
molecules of diflFerent kinds to combine together to form 
large quantities of molecules of a chemical compound ; and 

^ "Introduction to the Study of Chemical Philosophy," 1876, p. 4. 




6 OPEN-AIR STUDIES 

in either case, by weighing the quantity of each substance 
dealt with, we can find out in what proportions the elements 
are combined in any particular compound. 

We may now glance backwards, and define an atom as the 
smallest quantity of an element that can be driven out of or 
caused to enter into a molecule of a compound in the subtle 
process of destroying or producing any of the known chemical 
combinations of that element. Here we have got down as 
far as we can go in the chemical constitution of a mineral. 
Minerals are made of chemical substances, which are made 
of molecules ; these molecules consist of atoms either (a) of 
diflFerent kinds, in which case we are dealing with a com- 
pound, or (b) of only one kind, in which case our substance 
is an element. 

Now we may try to arrive at a definition of a mineral. 
Let us look at those which we have separated from the 
granite — three materials evidently requiring distinct names, 
evidently differing markedly in their physical characters. 

The clear little lumps are called QuartZy and do not tell us 
very much by their external appearance. They break across 
with irregular curving fractures, much as glass does; and 
they have in this case no regular shape. But they are trans- 
parent, and also very hard; for we cannot scratch them 
with a knife, and they, on the other hand, will scratch glass. 
Moreover, they will not soften and melt, as glass does, when 
held with a pair of forceps in the flame of a Bunsen burner 
— ^the gas-burner used in chemical laboratories or in ordinary 
gas-stoves. Clearly, they are not grains of glass. 

If we give them to a chemist, he will find in them the two 
elements, Silicon and Oxygen, always in the proportion of one 
atom of silicon to two atoms of oxygen. Quartz is made, in 
fact, of the oxide of silicon, commonly called Silica. We may 
take any of these grains from granite rocks found anywhere 
in the world, and yet their chemical composition will be the 
same. 

The dull white or pink bodies are called Orthoclase, or 
OrtJwclase Felspar ; these, as we have already noticed, have 
the property of breaking across regularly in certain direc- 
tions — in two directions, at any rate — ^when struck with a 
hammer. This shows that their internal structure, the way 
in which the molecules are grouped together, differs from 
of quartz. Moreover, we can see something of their 



THE MATERIALS OF THE EARTH 7 

external shape ; it is often regular, and, even on roughly 
broken surfaces of the rock, the larger orthoclases are seen 
to approach the form of small flat bricks. Then, in turning 
about the rock-specimen in the hand, some of these ortho- 
clases seem to be built up of two parts ; that is, one half of 
the orthoclase catches the light and gives a bright reflection, 
while the other half looks dull ; clearly the planes of fracture 
are differently sloped in the two parts of the mineral, and it 
has not a perfectly simple internal structure. 

A good knife will just scratch the orthoclase, if drawn 
firmly across it ; but orthoclase will scratch ordinary glass ; 
we thus learn that it is harder than glass, but not so hard as 
quartz. A little splinter of orthoclase can just be melted 
after holding it for some time in the flame of a Bunsen 
gas-burner. 

Our chemist tells us that this mineral is more complex 
than quartz. He finds in it Silicon, Oxygen, Aluminium, 
Potassium, and generally Sodium. The proportion of these 
elements to one another is always the same, except in the 
case of the two last named. Sometimes there is only potas- 
sium present, and no sodium ; sometimes sodium occurs, and 
then there is less potassium. We say that the potassium may 
be rcplcmd in part by sodium without the principal charac- 
teristics of the mineral being altered. In such cases it must 
be a matter of general consent and judgment as to whether 
we are to call the mineral by a new name when such a re- 
placement occurs. The atoms of sodium are lighter than 
those of potassium ; but any difference in the weight of a 
given bulk of orthoclase, according as it contains potassium, 
or both potassium and sodium, would be very trifling. Cases 
often occur, moreover, where a lighter element replaces a 
heavier one, and yet the resulting variety of the mineral is 
actually heavier than the ordinary form. The molecules con- 
taining the lighter element must in such cases lie closer 
together, i.e., there must be more of them in a given space, 
than occurs when only molecules containing the heavier 
element are present. 

So we may note that the chemical composition of some 
minerals may vary slightly, varieties being set up which are 
grouped together under the common mineral name. A mole- 
cule of our typical orthoclase contains 2 atoms of potassium, 
2 of aluminium, 6 of silicon, and i6 of oxygen. But in most 



LIST OF ILLUSTRATIONS 



FULL-PAGE ILLUSTRATIONS 



CwM-GLAS, Pass of Llanbebis 

PLATB 

I. Waterfall forming an Alcove in Stratified Rocks, 

Glencar, Go. Sligo 

II. Snow-filled Cirque at the base of the Matterhom, 

Switzerland 

III. Stratified Sands and Gravels, Antrim 
lY. The Sea breaking on a rocky coast, near Bally- 
castle, Go. Antrim 

V. The Grater-rim of the Pay de Pariou, Auvergne . 
YI. Golumns at the Giant's Gauseway, Go. Antrim, in 

Basaltic Lava-flow . . . . 
VIL Dyke of Dolerite, Quarry on Gave Hill, Belfast . 
VIII. Golumnar and massive Lava-flows at Pleaskin Head, 

Go. Antrim 

IX. Granite exposed on slope above the Eilkeel River, 

Moume Mountains, Go. Down .... 

X. Fossil Shells in Pliocene Sands, Felixstowe, Suffolk . 

XI. Gontorted Upper Jurassic Strata, Stare Gove, Lul- 

worth, Dorsetshire 



Frontispiece 



To faee page 42 



56 
76 

96 

'SO 

172 
181 

183 

220 



*l 



284 



ILLUSTRATIONS IN TEXT 

FIG. PAGE 

1. Pot-hole, Glenariff, Go. Antrim 31 

2. Section illustrating the origin of Springs 59 

3. Section showing principle of Artesian Springs and Wells, and 

origin of Bournes 60 

4. Section of Gorge choked with Alluvium 75 

5. Section showing a slope of i in 17 79 

xi 



• • 



XU LIST OF ILLUSTRATIONS 

FIO. PAOB 

6. Sections of Alpine valley and Scotch glens 83 

7. Old Lake-Terraces of the Salt-Lake area of Utah . . • 139 

8. The island of Ynlcano in eruption 155 

9. Small Cones thrown up on Etna 159 

la Section of a Volcano 161 

1 1. Floating Scorias above the Submarine Eruption off Fantelleria . 163 

12. Microscopic section of Obsidian 165 

13. Microscopic section of Basalt 167 

14. The Puy de Lassolas and the Puy de la Yache . . .176 

15. Geological Map, showing Lava-flows descending from Puys in 

Auvergne 177 

16. Granite Pinnacles, Mourne Mountains 193 

17. Unconformable Junction, with Overlap and Overstep . .219 

18. Internal cast of a Gerithium, Portland Stone . . .221 

19. a, Pecten Beaver i; b, Pecten cinctus; c, Pecten islandicus . 225 

20. Trilobites 235 

21. Section across the Surrey Hills 249 

22. Section illustrating Variation of Width of Outcrop . 253 

23. Sand with Spicules of Siliceous Sponges, Hythe Beds, Surrey 261 

24. Ancyloeeras gigas 269 

25. AcaiUKoceraB roihomagense 271 

26. Aetiiioeamax pUnus 273 

27. Inoceramus Cuvieri 274 

28. Section illustrating Fan-Structure in a Mountain-Chain . . 284 

29. Section illustrating Recumbent Folds 284 

30. Section across a Fault 285 

31. Plan of a Fault in inclined Strata 286 

32. Ridges and Valleys formed by Folds in the Jura Mountains 291 

33. Recumbent Synclinal and Folding on the WindgaUe . . 297 






- •» 



OPEN-AIR STUDIES 



•v.. 

• • • • 



.• • 



CHAPTER I 

THE MATERIALS OF THE EARTH 

When we were children, as soon as we could think and 
ask questions, most of us tried to find out two important 
matters — how to make things, and what things are made of. 
The little boy who cut open his drum to see where the sound 
came from was not so entirely foolish as is sometimes repre- 
sented, for he at least made an interesting and valuiable 
experiment. He learnt in this way that a drum was best 
constructed by stretching two thin skins opposite to one 
another, and shutting in a quantity of air between them. 
He was not satisfied with the mere showy outsides of things, 
or with the royal arms of Great Britain and Ireland painted 
on the wooden barrel of the drum. He felt that the sound, 
which was the great feature of the instrument, must have a 
cause ; and he set to work to find out something about it for 
himself. Probably he only got as far as seeing how the 
drum was made, and had to ask his father for the reason of 
this particular arrangement. But that is what every one has 
to do, and why no great discovery is likely to be of use to 
us unless we know what other people have previously dis- 
covered. In the same way, we cannot write a passably useful 
book unless we are near the 50,000 volumes of a well-stocked 
public library. Our knowledge in this world does not go on 
by jumps and bounds, but by a study of what others have 
seen and done, and of the records of their failure or success. 
Even if, after a long series of experiments, we have to leave 
our old drums damaged and cut open, we may soon have wit 
enough to make newer and better ones for the service of 
ourselves and our descendants. 



_ • 



• ' ■ 



LIST OF ILLUSTEATIONS 



FULL-PAGE ILLUSTRATIONS 



GwM-GLAs, Pass of Llanbebib 



PLATB 

I. Waterfall forming an Alcove in Stratified Bocks, 

Glencar, Go. Sligo 

II. Snow-filled Girqne at the base of the Matterhom, 
Switzerland 

III. Stratified Sands and Gravels, Antrim 

IV. The Sea breaking on a rocky coast, near Bally- 

castle, Go. Antrim 

V. The Grater-rim of the Pay de Pariou, Auvergne . 
YI. Golumns at the Giant's Gauseway, Go. Antrim, in 

Basaltic Lava-flow . . ... 
YIL Dyke of Dolerite, Quarry on Gave Hill, Belfast . 
YIII. Golumnar and massive Lava-flows at Pleaskin Head, 

Go. Antrim 

IX. Granite exposed on slope above the Eilkeel Biver, 

Mourne Mountains, Go. Down .... 

X. Fossil Shells in Pliocene Sands, Felixstowe, Suffolk . 

XI. Gontorted Upper Jurassic Strata, Stare Gove, Lul- 

worth, Dorsetshire 



Frontispiece 



To face page 42 



56 
76 

96 

172 
181 

183 

220 



*> 



284 



ILLUSTRATIONS IN TEXT 

FIG. PAGE 

1. Pot-hole, Glenariff, Go. Antrim 31 

2. Section illustrating the origin of Springs 59 

3. Section showing principle of Artesian Springs and Wells, and 

origin of Bournes 60 

4. Section of Gorge choked with Alluvium 75 

5. Section showing a slope of i in 17 79 

xi 



• • 



Xll LIST OF ILLUSTRATIONS 

no. PAOB 

6. Sections of Alpine valley and Scotch glens 83 

7. Old Lake-Terraces of the Salt-Lake area of Utah . . '139 

8. The island of Vnlcano in eruption 155 

9. Small Cones thrown up on Etna 159 

la Section of a Volcano 161 

11. Floating Scorias above the Submarine Eruption off Fantelleria . 163 

12. Microscopic section of Obsidian 165 

13. Microscopic section of Basalt 167 

14. The Fuy de Lassolas and the Puy de la Vache . . .176 

15. Geological Map, showing Lava-flows descending from Puys in 

Auvergne 177 

16. Granite Pinnacles, Moume Mountains 193 

17. Unconformable Junction, with Overlap and Overstep . .219 

18. Internal cast of a Cerithium, Portland Stone .221 

19. a, Peeten Beaver i; b, Peeten einctua; c. Peeten idandicus . 225 

20. Trilobites 235 

21. Section across the Surrey Hills 249 

22. Section illustrating Variation of Width of Outcrop . . 253 

23. Sand with Spicules of Siliceous Sponges, Hythe Beds, Surrey . 261 

24. Ancyloeera8 gigas 269 

25. Acantlioceraa roihomagense 271 

26. AetiiwcwnMx plenus 273 

27. Inoceramus Cuvieri 274 

28. Section illustrating Fan-Structure in a Mountain-Chain . 284 

29. Section illustrating Recumbent Folds 284 

30. Section across a Fault 285 

31. Plan of a Fault in inclined Strata 286 

32. Ridges and Valleys formed by Folds in the Jura Mountains . 291 

33. Recumbent Synclinal and Folding on the Windgalle . 297 






OPEN-AIR STUDIES 






CHAPTEE I 

THE MATERIALS OF THE EARTH 

When we were children, as soon as we conld think and 
ask questions, most of us tried to find out two important 
matters — how to make things, and what things are made of. 
The little boy who cut open his drum to see where the sound 
came from was not so entirely foolish as is sometimes repre- 
sented, for he at least made an interesting and valuable 
experiment. He leamt in this way that a drum was best 
constructed by stretching two thin skins opposite to one 
another, and shutting in a quantity of air between them. 
He was not satisfied with the mere showy outsides of things, 
or with the royal arms of Great Britain and Ireland painted 
on the wooden barrel of the drum. He felt that the sound', 
which was the great feature of the instrument, must have a 
cause ; and he set to work to find out something about it for 
himself. Probably he only got as far as seeing how the 
drum was made, and had to ask his father for the reason of 
this particular arrangement. But that is what every one has 
to do, and why no great discovery is likely to be of use to 
ns unless we know what other people have previously dis- 
covered. In the same way, we cannot write a passably useful 
book unless we are near the 50,000 volumes of a well-stocked 
public library. Our knowledge in this world does not go on 
by jumps and bounds, but by a study of what others have 
seen and done, and of the records of their failure or success. 
Even if, after a long series of experiments, we have to leave 
our old drums damaged and cut open, we may soon have wit 
enough to make newer and better ones for the service of 
ourselves and our descendants. 

k 



• • 



XU UST OF ILLUSTRATIONS 

FIG. PAOI 

6. Sections of Alpine valley and Scotch glens 83 

7. Old Lake-Terraces of the Salt-Lake area of Utah . '139 

8. The island of Vulcano in eruption 155 

9. Small Cones thrown up on Etna 159 

la Section of a Volcano 161 

1 1. Floating Scoriss above the Submarine Eruption off Fantelleria . 163 

12. Microscopic section of Obsidian 165 

13. Microscopic section of Basalt 167 

14. The Puy de Lassolas and the Puy de la Vache . . .176 

15. Geological Map, showing Lava-flows descending from Fuys in 

Auvergne 177 

16. Granite Pinnacles, Mourne Mountains 193 

17. Unconformable Junction, with Overlap and Overstep . 219 

18. Internal cast of a Cerithium, Portland Stone .... 221 

19. a, Peeten Beaver i; b. Pecten einctua; c, Peeten idandicus . 225 

20. Trilobites 235 

21. Section across the Surrey Hills 249 

22. Section illustrating Variation of Width of Outcrop . . 253 

23. Sand with Spicules of Siliceous Sponges, Hythe Beds, Surrey . 261 

24. Aneyloeeras gigas 269 

25. AcantJioceraa rothomagense 271 

26. AeUiMcamxix plenua 273 

27. Inoceramus Cuvieri 274 

28. Section illustrating Fan-Structure in a Mountain-Chain . 284 

29. Section illustrating Recumbent Folds 284 

30. Section across a Fault 285 

31. Plan of a Fault in inclined Strata 286 

32. Ridges and Valleys formed by Folds in the Jura Mountains 291 

33. Recumbent Synclinal and Folding on the Windgalle . -297 



>•' 



" • 



OPEN-AIR STUDIES O 



CHAPTEE I 

THE MATERIALS OF THE EARTH 

When we were children, as soon as we could think and 
ask questions, most of us tried to find out two important 
matters — how to make things, and what things are made of. 
The little boy who cut open his drum to see where the sound 
came from was not so entirely foolish as is sometimes repre- 
sented, for he at least made an interesting and valuable 
experiment. He learnt in this way that a drum was best 
constructed by stretching two thin skins opposite to one 
another, and shutting in a quantity of air between them. 
He was not satisfied with the mere showy outsides of things, 
or with the royal arms of Great Britain and Ireland painted 
on the wooden barrel of the drum. He felt that the sound", 
which was the great feature of the instrument, must have a 
cause ; and he set to work to find out something about it for 
himself. Probably he only got as far as seeing how the 
drum was made, and had to ask his father for the reason of 
this particular arrangement. But that is what every one has 
to do, and why no great discovery is likely to be of use to 
us unless we know what other people have previously dis- 
covered. In the same way, we cannot write a passably useful 
book unless we are near the 50,000 volumes of a well-stocked 
public library. Our knowledge in this world does not go on 
by jumps and bounds, but by a study of what others have 
seen and done, and of the records of their failure or success. 
Even if, after a long series of experiments, we have to leave 
our old drums damaged and cut open, we may soon have wit 
enough to make newer and better ones for the service of 
ourselves and our descendants. 



t • 



OPEN-AIR STUDIES 



••..' 



Ii^-emj times, it was most important that man should 
find but how to make things. He had to build shelters 
againsj^'the rain; he had to find weapons with which to 
cqiilh4^ ^^^ wild beasts ; he had to carve out gourds into 
yes^s in which liquids could be carried. But all these 
.thin'gs were by no means easy, and required a good deal of 
•.ol^ervation. Nature was already doing many wonderful 
r*Vttings in the great world round about, and it was well to 
..'watch, and even to imitate, these closely. After all, what- 
• • ever was required by man had to be made out of natural 
materials. One result of this struggle with diflSculties was 
that early man took to studying the stones beneath his feet. 
Some of his earliest instruments were made of stone ; and 
we know that many savage tribes have only given up the 
use of stone axes and stone arrow-heads since the arrival of 
European traders on their coasts. Primitive peoples would 
soon observe that some kinds of stone break more easily 
than others, that some kinds can be chipped in almost any 
direction so as to give a sharp cutting edge, and that some, 
again, are far superior in hardness or durability to the 
rest. It became important to search among the rocks for 
materials suited to each special purpose ; and thus began, 
perhaps, the first researches into the structure of the world 
around ua 

When native metals were discovered, and when, moreover, 
it was found that valuable substances could be extracted by 
heat from stones utterly unlike them in appearance, the 
study of the earth became a much more complicated matter ; 
and at last a few thoughtful persons took to inquiring how 
such-and-such materials, used by man in the manufacture of 
common things, came themselves to be made in the heart of 
the old solid earth. Then began the science of Oeology, tbe 
systematic study of the way in which the world is built up, 
and of the natural changes which go on within it and upon it. 
Even the earliest men must have seen that the earth 
changed around them. Floods came down, and covered 
smiling landscapes with sand and stones from distant hills ; 
volcanoes broke out, and heaped ashes and lava upon the 
surface ;; the sea worked against the land, and washed the 
coast steadily away ; while in other places tawny rivers wan- 
dered through the plains and thrust their burden of mud in 
long banks far to seaward. 



THE MATERIALS OF THE EARTH 3 

Thus the earth changed its surface, growing at one 
place, decaying away at another ; and men began to realise 
that it had a history, beside which their own lives were short 
indeed. And yet it is only in the last hundred years or so 
that we have been able to read this history at all clearly, 
and even now we understand only that end of it which lies 
nearest to ourselves. 

Before we go out and try to read a page or two of this 
history, we must learn something of the materials with 
which we have to deal. Of what, then, is the earth actually 
made? 

As a matter of fact, we know only a very small part of 
the vast globe on which we live. The centre of the earth 
lies 4000 miles beneath us, and our mines and borings pene- 
trate the great mass to a depth of only about a mile. But, 
as we shall see later, the outer layers of the earth have 
become wrinkled and folded, so that rocks which once lay 
far below the surface have been brought up within our 
reach. Hence in some places, immediately under the loose 
soil, we may find materials which were formerly ten or 
fifteen miles lower down; and this enables us to say that 
we have some idea of the constitution of the globe to a 
depth of fifteen miles from the surface. It is not much, 
this mere outer shell, fifteen miles thick all round the 
earth; but it is all we shall have to deal with, and we 
speak of this accessible region as the crust of the earth. 

This solid crust is made of rocks. Any workman in a 
quarry will tell us, for instance, that granite is a rock, or 
that sandstone is a rock. But, when we examine these two 
materials, we see that they are made up of distinct particles 
which themselves are worth inquiring into. The granite 
has clear little lumps, like glass, in it ; and dull white or 
pink bodies, which seem to break across in a regular manner, 
with smooth or step- like surfaces ; and soft flaky things 
which reflect the light brilliantly, and which can be pulled 
away, or dog out with a knife, in the form of little shining 
plates. The sandstone, on the other hand, is made of 
practically one kind of material throughout, in the form of 
a number of hard and somewhat rounded grains. 

In each case we call these constituents, having characters 
of their own, the minerals which compose the rock. The 
granite consists of at least three distinct minerals, the sand- 



4 OPEN-AIR STUDIES 

stone of only one. Now, if we break up a rock, and select 
a number of fragments of any one kind of mineral, a chemist 
will show us that this mineral is itself made up of certain 
chemical substances, which he can separate and accurately 
determine. He will be able to find out in what proportions 
these chemical substances are present, and will thus give us 
an account of the chemical constitution of the mineral. 

But what about these various substances? They may 
be stated by our friendly chemist to be chemical compounds, 
and these can be further split up into their elements. Or, to 
take the simplest case, our mineral may possibly consist of 
merely one element. 

Here we may remind ourselves of some of our chemical 
notions. We must go back, indeed, to the foundations of 
several sciences for the correct understanding of our rocks, 
and this first chapter is going to be a serious one, before we 
can fairly get out into the country and the open air. But 
we must remember that all the things with which we shall 
deal are quite natural, all come from the earth itself that 
stretches round us ; and those parts of chemistry and physics 
which are possibly a little dull to us seem so merely because 
we cannot handle or directly observe the things about which 
we are being told. If we could see the tiny '' atoms " 
moving in the " molecule " of a substance, we should pro- 
bably be as delighted and as fascinated as if we were sitting 
on a mountain-peak and watching the great balance of the 
stars. 

A chemical element is a substance that cannot be split 
up, by any means at present in our power, into any other 
substances with different properties from those by which it 
is itself characterised. It is thus the simplest kind of 
material known to us. Gold, silver, copper, and iron are 
elements; sulphur is an element; so also is carbon, well 
known to us in its commonest form, the " black-lead '' of 
our pencils. There are now about seventy elements known, 
and others, at present doubtful, are likely to be added to 
the list. 

The ancients regarded the earth as an element in itself, 
something existing as a foundation for other things, the 
remaining elements being air, fire, and water. What we 
now know as elements were often treated in earlier times 
as varied forms of the same fundamental material ; but all 



THE MATERIALS OP THE EARTH S 

experiment has shown us up to the present that there are 
really, in this earth and throughout the mighty universe, a 
number of different kinds of matter. To be quite simple in 
our conceptions, we might wish to say that all elements are 
made up of different arrangements of particles of one first- 
formed matter ; but that would be merely guess-work, and 
at present we cannot get beyond our seventy elements. 

If we conceive the smallest particle of an element that 
can independently exist, we may call such a particle an 
atom. It will have a certain weight, and the atoms of 
different elements differ in their weights. But any quantity 
of matter that we can see, even with a microscope, must 
consist of enormous numbers of atoms. 

The atoms are said to be grouped together in molecules, 
or " little masses." Chemists regard the molecule of certain 
elements as consisting of only one atom ; in others, two or 
even six atoms may form the molecule. A molecule has 
been defined by Professor Tilden as " the smallest quantity 
which is able to take part in or result from a chemical 
change."^ 

A chemical compound is built up of molecules, each of 
which consists of atoms of more than one kind. In the 
simplest compounds the molecule consists of only two 
atoms, one atom of one element being combined with one 
of another. The elements have been shown to combine 
together in fixed proportions, forming compounds with dis- 
tinctive properties. We may hence say that the molecule 
of a compound is the smallest particle into which the sub- 
stance could be divided while yet retaining its peculiar 
chemical constitution. Further splitting might give us cer- 
tain simpler compounds; but ultimately the actual atoms, 
or groups of similar atoms, of each molecule would be set 
free ; in other words, the compound would separate into 
its elements. 

All this may seem beyond human observation ; but large 
quantities of molecules of a compound can be dealt with in 
our experiments, and large quantities of elementary molecules 
can be extracted by chemical processes from them. Or, on 
the other hand, we can cause large quantities of elementary 
molecules of different kinds to combine together to form 
large quantities of molecules of a chemical compound ; and 

^ "Introduction to the Study of Chemical Philosophy," 1876, p. 4. 




6 OPEN-AIR STUDIES 

in either case, by weighing the quantity of each substance 
dealt with, we can find out in what proportions the elements 
are combined in any particular compound. 

We may now glance backwards, and define an atom as the 
smallest quantity of an element that can be driven out of or 
caused to enter into a molecule of a compound in the subtle 
process of destroying or producing any of the known chemical 
combinations of that element. Here we have got down as 
far as we can go in the chemical constitution of a mineral. 
Minerals are made of chemical substances, which are made 
of molecules ; these molecules consist of atoms either (a) of 
different kinds, in which case we are dealing with a com- 
pound, or (b) of only one kind, in which case our substance 
is an element. 

Now we may try to arrive at a definition of a mineral. 
Let us look at those which we have separated from the 
granite — three materials evidently requiring distinct names, 
evidently differing markedly in their physical characters. 

The clear little lumps are called Qiiartz, and do not tell us 
very much by their external appearance. They break across 
with irregular curving fractures, much as glass does ; and 
they have in this case no regular shape. But they are trans- 
parent, and also very hard; for we cannot scratch them 
with a knife, and they, on the other hand, will scratch glass. 
Moreover, they will not soften and melt, as glass does, when 
held with a pair of forceps in the flame of a Bunsen burner 
— the gas-burner used in chemical laboratories or in ordinary 
gas-stoves. Clearly, they are not grains of glass. 

If we give them to a chemist, he will find in them the two 
elements, Silicon and Oxygen, always in the proportion of one 
atom of silicon to two atoms of oxygen. Quartz is made, in 
fact, of the oxide of silicon, commonly called Silica. We may 
take any of these grains from granite rocks found anywhere 
in the world, and yet their chemical composition will be the 
same. 

The dull white or pink bodies are called Orthoclase, or 
Orthoclase Felspar ; these, as we have already noticed, have 
the property of breaking across regularly in certain direc- 
tions — in two directions, at any rate — when struck with a 
hammer. This shows that their internal structure, the way 

jRthich the molecules are grouped together, differs from 
of quartz. Moreover, we can see something of their 



THE MATERIALS OF THE EARTH 7 

external shape; it is often regular, and, even on roughly 
broken surfaces of the rock, the larger orthoclases are seen 
to approach the form of small flat bricks. Then, in turning 
about the rock-specimen in the hand, some of these ortho- 
clases seem to be built up of two parts ; that is, one half of 
the orthoclase catches the light and gives a bright reflection, 
while the other half looks dull ; clearly the planes of fracture 
are differently sloped in the two parts of the mineral, and it 
has not a perfectly simple internal structure. 

A good knife will just scratch the orthoclase, if drawn 
firmly across it ; but orthoclase will scratch ordinary glass ; 
we thus learn that it is harder than glass, but not so hard as 
quartz. A little splinter of orthoclase can just be melted 
after holding it for some time in the flame of a Bunsen 
gas-burner. 

Our chemist tells us that this mineral is more complex 
than quartz. He finds in it Silicon, Oxygen, Aluminium, 
Potassium, and generally Sodium. The proportion of these 
elements to one another is always the same, except in the 
case of the two last named. Sometimes there is only potas- 
sium present, and no sodium ; sometimes sodium occurs, and 
then there is less potassium. We say that the potassium may 
be replaced in part by sodium without the principal charac- 
teristics of the mineral being altered. In such cases it must 
be a matter of general consent and judgment as to whether 
we are to call the mineral by a new name when such a re- 
placement occurs. The atoms of sodium are lighter than 
those of potassium ; but any difference in the weight of a 
given bulk of orthoclase, according as it contains potassium, 
or both potassium and sodium, would be very trifling. Gases 
often occur, moreover, where a lighter element replaces a 
heavier one, and yet the resulting variety of the mineral is 
actually heavier than the ordinary form. The molecules con- 
taining the lighter element must in such cases lie closer 
together, i.e., there must be more of them in a given space, 
than occurs when only molecules containing the heavier 
element are present. 

So we may note that the chemical composition of some 
minerals may vary slightly, varieties being set up which are 
grouped together under the common mineral name. A mole- 
cule of our typical orthoclase contains 2 atoms of potassium, 
2 of aluminium, 6 of silicon, and i6 of oxygen. But in most 



8 OPEN-AIR STUDIES 

specimens of orthoclase there are some molecules in which 
two atoms of sodium take the place of the two atoms of potas- 
sium. When such molecules are shown by a chemical analysis 
to be numerous, we call the mineral variety Soda-Orthoclase. 

Our third mineral in the granite is called Mica — the plate- 
like substance which is easily dug out with the knife, and 
which gives such a shining appearance to many specimens of 
the rock. Some micas are pale and silvery ; others are quite 
dark, being bronze-coloured or black ; but they have many 
characters in common. Again and again their proper form 
can be seen ; their molecules are clearly capable of building 
up six-sided plates. This structure is so common that it can- 
not be accidental ; and careful measures show that the angles 
of the hexagonal figure are kept the same in the same chemical 
variety. Such a structure is called a crystal ; and a little 
observation will show us that the orthoclase also is in the 
form of crystals, though they have probably not been able to 
grow to such perfection. The mica splits very easily in one 
direction, so that we can flake off thin flexible plates ; and 
even the blacker micas are no longer opaque when one of their 
thin plates is held up to the light. The mineral is quite soft, 
and can often be scratched by the thumb-nail. 

The chemical composition of the micas is still more 
complex than that of the orthoclase felspar, but all common 
varieties contain Silicon, Oxygen, Aluminium, Potassium, 
Magnesium, Iron, and Hydrogen. The pale varieties con- 
tain little iron and usually little magnesium ; the dark 
varieties are richer in these elements and poorer in silicon 
and aluminium. There may be a good deal of replacement 
of one element by another in the mica series, the general 
external characters being retained ; and several different 
kinds or species of mica are recognised, and are known by 
distinct mineral names. 

If we are so fortunate as to find a granite with a number 
of small hollows in it, perhaps half-an-inch or an inch across, 
such as occur in the famous rocks of the northern part of 
the Mourne Mountains, then we may see that all the 
minerals which we have discussed are capable of forming 
crystals, wherever freedom is given to them and when they 
are not too much squeezed together. In such hollows we 
the mica, and the orthoclase, and the quartz itself, 
y crystallised, beautifully and regularly shaped, so 




THE MATERIALS OF THE EARTH 9 

that persons looking at the handsome crystals in public 
collections often think that they have been artificially cut 
and polished. But you have only to go into the hills, and 
search in cracks and hollows for yourselves, to find that 
crystals occur naturally, and that they are, indeed, the form 
frequently adopted by natural chemical substances. And, 
further, the crystals of one compound usually differ from 
those of another ; the sides make different angles one with 
another, even if the forms are very much alike; so that, 
by careful observation and measurement of the angles in 
various crystals, we can use the outer shape to help us in 
determining the nature of the mineral. 

And now we can at last arrive at our definition. A 

mineral is a natural substance, formed without the action of 

plants or animals. Its chemical composition is constant, or 

vaiiM only hy a well-defined series of ch/imical replacements. 

Under favourable conditions, it assumes a crystalline form. 

One mineral is known from another by a number of 
characters which must be considered all together; and 
these will be found stated in any text-book of mineralogy.^ 
Let us run over the most important of these characters 
here. 

I . Colour. — When there are several minerals in a rock, 
this character often clearly marks out one from another. 
But it is of far less importance than might be supposed, 
since many common minerals are coloured by some trifling 
impurity; a sort of stain runs through them, as it were, 
and in their pure condition they are colourless. Metallic 
ores, however, usually have characteristic colours ; thus Iron 
Pyrites, the common iron sulphide, is brass-yellow, and 
Native Copper, the natural element, is copper-red. But, on 
the other hand, the red gem Ruby and the blue Sapphire are 
mere varieties of the same mineral species. Corundum, the 
composition of both being aluminium oxide coloured by a 
substance very insignificant in amount.^ Hence we must 

^ Such as Hatch, "Mineralogy" (Whittaker & Co.) ; Rutley, "Mineralogy" 
(T. Murby). 

'^ Artificial corundum has been coloured red (ruby) by adding chromium 
fluoride to the materials employed ; and, curiously enough, the addition of 
this same substance in varying proportions has given rise to sapphires and to 
a green variety. Rubies have also been made by adding potassium bichro- 
mate, and sapphires by adding cobalt oxide (Fouqud and L^vy, Synthase 
des MiiUraux et des Hoches, pp. 220 and 222). 



lO OPEN- AIR STUDIES 

rely on other characters besides ccdoar in the determining 
of a mineral species. 

2. Transparencj or Opacity. — Some minerals are 
characteristicstlly transparent — in thin flakes, at any rate. 
Here, again, imparities, and chemical changes as the mineral 
alters or decays, may render a clear substance finally opaque. 
Calcite (caldnm carbonate) is typically transparent; Lron 
Pyrites is opaqne, even when ground down thinner than a 
sheet of notepaper. 

3. Lustre. — Some minerals reflect light brilliantly, like 
Quartz and Bock-Salt, which are said to have a ''glassy 
lustre," because of their resemblance in this respect to glass. 
Others, as Iron Pyrites, look like polished metal, and are 
said to have a ''metallic lustre." Others are quite dull and 
earthy, like Wad, one of the hydrous manganese oxides. 

4. Malleability and Brittleness. — Some minerals can 
be hammered out without breaking, and are said to be 
"malleable," as Native Gold. Others are brittle, and fly 
to pieces when struck, as Iron Pyrites or Quartz. 

5. Hardness. — This is one of the most important and 
useful characters. A mineral may be brittle, and yet may 
be soft enough to be cut into with a knife, like Copper 
Pyrites (sulphide of copper and iron) ; or it may be brittle, 
and yet too hard to be scratched with a knife, like Iron 
l^yrites. For our present purposes, we may note three kinds 
of hardness among minerals : — 

a. Some minerals cannot be scratched by a good knife. 
6. Some minerals can be scratched by a knife, but not 

by the thumb-nail, 
c. Some minerals can be scratched by the thumb-nail. 

Sometimes, in examining our rocks, it is difficult to 
Bay if some small projecting grain is hard or soft; we 
cannot determine whether we can scratch it, for fear of 
demolishing it or removing it altogether. In such cases 
we rany draw it across the side of the knife-blade or across 
our thumb-nail, and see if it scratches either of these, in 

^case it is harder than the substance scratched. If 
leral is in the form of loose grains, like those broken 
•andstone, they can be stuck on to a piece of wood by 
hn cement, such as the old bicycle-tyre cement, with 
lArp little points sticking out above the surface ; and 



THE MATERIALS OF THE EARTH I I 

then, held by this handle, we can draw them across the 
knife or across the thumb-nail. Another plan is to squeeze 
them between two plates of glass, such as the slips used for 
mounting microscopic objects ; it is easy then to see whether 
the little grains are scratching the surface of the glass. 

6. Streak. — ^The colour of the powder of a mineral, 
produced by cutting into it or by crushing it out under 
a clean hammer upon white paper, is called its "streak." 
Every time that we use an ordinary pencil we see the 
streak of Graphite (one form of carbon), the mineral known 
popularly as ** black-lead." 

7. Flexibility. — Some minerals can be bent, especially 
in thin flakes, and remain in the form thus given to them. 
They are then said to be " flexible." 

8. Elasticity. — Other minerals are said to be " elastic," 
when, like Mica, they spring back into their former shape 
after being bent. 

9. Specific Gravity. — The statement of the Specific 
Gravity of a substance expresses its relative weight as com- 
pared with pure water at a temperature — in most English 
experiments — of 60° F. If we say that a mineral has a 
specific gravity of 3, we mean that any given bulk of it 
is three times as heavy as an equal bulk of water at 
60° P. A cubic inch of it would thus weigh as much as 
three cubic inches of water at that temperature. Most 
minerals of common occurrence have a specific gravity be- 
tween 2 and 3.5. Meerschaum, used for the bowls of pipes, 
is as low as 1.5, while Gold is as high as 19.3, and a native 
alloy of Platinum and Iridium actually reaches 23. 

In the beautiful system of weights and measures in- 
vented in France, and now used by almost all civilised 
peoples, the specific gravity of a mineral or a rock at once 
tells us how much space a given weight of it will occupy, 
or, on the other hand, how much a given bulk of it will 
weigh. In this system the weight known as I gramme is the 
weight of a bulk of water occupying i cubic centimetre at a 
temperature of 4° C. Hence, adopting this temperature for 
the experiments, i gramme of a substance of a specific 
gravity of 5 will occupy i-Sth of a cubic centimetre, or 200 
cubic millimetres, and 100 grammes of it will occupy 20 
cubic centimetres. On the other hand, to take another 
example, 7CX:) cubic centimetres of a mineral with a specific 



« • 



OPEN-AIR STUDIES 



• " ., 



Ijx: etaij times, it was most important that man should 
find but how to make things. He had to build shelters 
agaJHs/S'the rain; he had to find weapons with which to 
cqiilh^^ ^^^ ^^^ beasts ; he had to carve out gourds into 
yes^s in which liquids could be carried. But all these 
.thin'gs were by no means easy, and required a good deal of 
•".ol^ervation. Nature was already doing many wonderful 
r*Vt4ings in the great world round about, and it was well to 
..'watch, and even to imitate, these closely. After all, what- 
• • ever was required by man had to be made out of natural 
materials. One result of this struggle with diflSculties was 
that early man took to studying the stones beneath his feet. 
Some of his earliest instruments were made of stone ; and 
we know that many savage tribes have only given up the 
use of stone axes and stone arrow-heads since the arrival of 
European traders on their coasts. Primitive peoples would 
soon observe that some kinds of stone break more easily 
than others, that some kinds can be chipped in almost any 
direction so as to give a sharp cutting edge, and that some, 
again, are far superior in hardness or durability to the 
rest. It became important to search among the rocks for 
materials suited to each special purpose ; and thus began, 
perhaps, the first researches into the structure of the world 
around ua 

When native metals were discovered, and when, moreover, 
it was found that valuable substances could be extracted by 
heat from stones utterly unlike them in appearance, the 
study of the earth became a much more complicated matter ; 
and at last a few thoughtful persons took to inquiring how 
such-and-such materials, used by man in the manufacture of 
common things, came themselves to be made in the heart of 
the old solid earth. Then began the science of Oeology, tbe 
systematic study of the way in which the world is built up, 
and of the natural changes which go on within it and upon it. 
Even the earliest men must have seen that the earth 
changed around them. Floods came down, and covered 
smiling landscapes with sand and stones from distant hills ; 
volcanoes broke out, and heaped ashes and lava upon the 
surface ;: the sea worked against the land, and washed the 
coast steadily away ; while in other places tawny rivers wan- 
dered through the plains and thrust their burden of mud in 
long banks far to seaward. 



THE MATERIALS OF THE EARTH 3 

Thus the earth changed its surface, growing at one 
place, decaying away at another ; and men began to realise 
that it had a history, beside which their own lives were short 
indeed. And yet it is only in the last hundred years or so 
that we have been able to read this history at all clearly, 
and even now we understand only that end of it which lies 
nearest to ourselves. 

Before we go out and try to read a page or two of this 
history, we must learn something of the materials with 
which we have to deal. Of what, then, is the earth actually 
made? 

As a matter of fact, we know only a very small part of 
the vast globe on which we live. The centre of the earth 
lies 4000 miles beneath us, and our mines and borings pene- 
trate the great mass to a depth of only about a mile. But, 
as we shall see later, the outer layers of the earth have 
become wrinkled and folded, so that rocks which once lay 
far below the surface have been brought up within our 
reach. Hence in some places, immediately under the loose 
soil, we may find materials which were formerly ten or 
fifteen miles lower down; and this enables us to say that 
we have some idea of the constitution of the globe to a 
depth of fifteen miles from the surface. It is not much, 
this mere outer shell, fifteen miles thick all round the 
earth; but it is all we shall have to deal with, and we 
speak of this accessible region as the crust of the earth. 

This solid crust is made of rocks. Any workman in a 
quarry will tell us, for instance, that granite is a rock, or 
that sandstone is a rock. But, when we examine these two 
materials, we see that they are made up of distinct particles 
which themselves are worth inquiring into. The granite 
has clear little lumps, like glass, in it ; and dull white or 
pink bodies, which seem to break across in a regular manner, 
with smooth or step- like surfaces ; and soft fiaky things 
which reflect the light brilliantly, and which can be pulled 
away, or dug out with a knife, in the form of little shining 
plates. The sandstone, on the other hand, is made of 
practically one kind of material throughout, in the form of 
a number of hard and somewhat rounded grains. 

In each case we call these constituents, having characters 
of their own, the minerals which compose the rock. The 
granite consists of at least three distinct minerals, the sand- 



LIST OF ILLUSTRATIONS 



FULL-PAGE ILLUSTRATIONS 



CwM-GLAB, Pass of Llanbebis 



PLATB 

I. Waterfall forming an Alcove in Stratified Bocks« 

Glencar, Co. Sligo 

II. Snow-filled Cirque at the base of the Matterhom, 
Switzerland 

III. Stratified Sands and Gravels, Antrim 

IV. The Sea breaking on a rocky coast, near Bally- 

castle, Co. Antrim 

V. The Crater-rim of the Pay de Pariou, Auvergne . 
VI. Columns at the Giant's Causeway, Co. Antrim, in 

Basaltic Lava-flow . . . . 
VIL Dyke of Dolerite, Quarry on Cave Hill, Belfast 
VIII. Columnar and massive Lava-flows at Pleaskin Head, 

Co. Antrim 

IX. Granite exposed on slope above the Kilkeel River, 

Mourne Mountains, Co. Down .... 

X. Fossil Shells in Pliocene Sands, Felixstowe, Suffolk . 

XI. Contorted Upper Jurassic Strata, Stare Cove, Lul- 

worth, Dorsetshire 



FronUtpiece 



To face page 42 



56 
76 

96 
150 

172 
181 

183 

190 
220 



»> 



284 



ILLUSTRATIONS IN TEXT 

no. PACK 

1. Pot-hole, Glenariff, Co. Antrim 31 

2. Section illustrating the origin of Springs 59 

3. Section showing principle of Artesian Springs and Wells, and 

origin of Bournes 60 

4. Section of Gorge choked with Alluvium 75 

5. Section showing a slope of i in 17 *\<^ 

xi 



XU LIST OF ILLUSTRATIONS 

FIO. PAQK 

6. Sections of Alpine valley and Scotch glens 83 

7. Old Lake-Terraces of the Salt-Lake area of Utah . . '139 

8. The island of Vulcano in eruption 155 

9. Small Cones thrown up on Etna 159 

la Section of a Volcano 161 

11. Floating Scorias above the Submarine Eruption off Fantelleria . 163 

12. Microscopic section of Obsidian 165 

13. Microscopic section of Basalt 167 

14. The Puy de Lassolas and the Puy de la Vache . .176 

15. Geological Map, showing Lava-flows descending from Puys in 

Auvergne 177 

16. Granite Pinnacles, Mourne Mountains 193 

17. Unconformable Junction, with Overlap and Overstep . .219 
i8r Internal cast of a Cerithium, Portland Stone . .221 

19. a. Peeten Beaver i; b, Pecten einctus; c, Pecten idandums . 225 

20. Trilobites 235 

21. Section across the Surrey Hills 249 

22. Section illustrating Variation of Width of Outcrop 253 

23. Sand with Spicules of Siliceous Sponges, Hythe Beds, Surrey . 261 

24. Aneyloeeras gigas 269 

25. Aca/rUlioeeras rothomagense 271 

26. AeUiwcamMx pUnus 273 

27. Inoceramu8 Cuvieri 274 

28. Section illustrating Fan-Structure in a Mountain-Chain . 284 

29. Section illustrating Recumbent Folds 284 

30. Section across a Fault 285 

31. Plan of a Fault in inclined Strata 286 

32. Ridges and Valleys formed by Folds in the Jura Mountains 291 

33. Recumbent Synclinal and Folding on the Windgalle . . 297 



■ : • 



OPEN-AIE STUDIES 



»• • • 



•• • 

• •_ > 



.• • 



• . • 



CHAPTER I 

THE MATERIALS OF THE EARTH 

When we were children, as soon as we could think and 
ask questions, most of us tried to find out two important 
matters — how to make things, and what things are made of. 
The little boy who cut open his drum to see where the sound 
came from was not so entirely foolish as is sometimes repre- 
sented, for he at least made an interesting and valuable 
experiment. He learnt in this way that a drum was best 
constructed by stretching two thin skins opposite to one 
another, and shutting in a quantity of air between them. 
He was not satisfied with the mere showy outsides of things, 
or with the royal arms of Great Britain and Ireland painted 
on the wooden barrel of the drum. He felt that the sound', 
which was the great feature of the instrument, must have a 
cause ; and he set to work to find out something about it for 
himself. Probably he only got as far as seeing how the 
drum was made, and had to ask his father for the reason of 
this particular arrangement. But that is what every one has 
to do, and why no great discovery is likely to be of use to 
us unless we know what other people have previously dis- 
covered. In the same way, we cannot write a passably useful 
book unless we are near the 50,000 volumes of a well-stocked 
public library. Our knowledge in this world does not go on 
by jumps and bounds, but by a study of what others have 
seen and done, and of the records of their failure or success. 
Even if, after a long series of experiments, we have to leave 
our old drums damaged and cut open, we may soon have wit 
enough to make newer and better ones for the service of 
ourselves and our descendants. 



» 



• 



•- 



« • 



OPEN-AIR STUDIES 



Ii\- e&riy times, it was most important that man should 
find but how to make things. He had to build shelters 
against" the rain; he had to find weapons with which to 
cqiilbi^ ^h® wild beasts ; he had to carve out gourds into 
ves^s in which liquids could be carried. But all these 
.thin'gs were by no means easy, and required a good deal of 
•.ol^ervation. Nature was already doing many wonderful 
r'Vtfdngs in the great world round about, and it was well to 
•.'watch, and even to imitate, these closely. After all, what- 
• • ever was required by man had to be made out of natural 
materials. One result of this struggle with difficulties was 
that early man took to studying the stones beneath his feet. 
Some of his earliest instruments were made of stone ; and 
we know that many savage tribes have only given up the 
use of stone axes and stone arrow-heads since the arrival of 
European traders on their coasts. Primitive peoples would 
soon observe that some kinds of stone break more easily 
than others, that some kinds can be chipped in almost any 
direction so as to give a sharp cutting edge, and that some, 
again, are far superior in hardness or durability to the 
rest. It became important to search among the rocks for 
materials suited to each special purpose ; and thus began, 
perhaps, the first researches into the structure of the world 
around ua 

When native metals were discovered, and when, moreover, 
it was found that valuable substances could be eirbracted by 
heat from stones utterly unlike them in appearance, the 
study of the earth became a much more complicated matter ; 
and at last a few thoughtful persons took to inquiring how 
such-and-such materials, used by man in the manufacture of 
common things, came themselves to be made in the heart of 
the old solid earth. Then began the science of Qeology, the 
systematic study of the way in which the world is built up, 
and of the natural changes which go on within it and upon it. 
Even the earliest men must have seen that the earth 
changed around them. Floods came down, and covered 
smiling landscapes with sand and stones from distant hills ; 
volcanoes broke out, and heaped ashes and lava upon the 
surface ;: the sea worked against the land, and washed the 
coast steadily away ; while in other places tawny rivers wan- 
dered through the plains and thrust their burden of mud in 
long banks far to seaward. 



THE MATERIALS OF THE EARTH 3 

Thus the earth changed its surface, growing at one 
place, decaying away at another ; and men began to realise 
that it had a history, beside which their own lives were short 
indeed. And yet it is only in the last hundred years or so 
that we have been able to read this history at all clearly, 
and even now we understand only that end of it which lies 
nearest to ourselves. 

Before we go out and try to read a page or two of this 
history, we must learn something of the materials with 
which we have to deal. Of what, then, is the earth actually 
made? 

As a matter of fact, we know only a very small part of 
the vast globe on which we live. The centre of the earth 
lies 4CXD0 miles beneath us, and our mines and borings pene- 
trate the great mass to a depth of only about a mile. But, 
as we shall see later, the outer layers of the earth have 
become wrinkled and folded, so that rocks which once lay 
far below the surface have been brought up within our 
reach. Hence in some places, immediately under the loose 
soil, we may find materials which were formerly ten or 
fifteen miles lower down; and this enables us to say that 
we have some idea of the constitution of the globe to a 
depth of fifteen miles from the surface. It is not much, 
this mere outer shell, fifteen miles thick all round the 
earth ; but it is all we shall have to deal with, and we 
speak of this accessible region as the crust of the earth. 

This solid crust is made of rocks. Any workman in a 
quarry will tell us, for instance, that granite is a rock, or 
that sandstone is a rock. But, when we examine these two 
materials, we see that they are made up of distinct particles 
which themselves are worth inquiring into. The granite 
has clear little lumps, like glass, in it ; and dull white or 
pink bodies, which seem to break across in a regular manner, 
with smooth or step- like surfaces ; and soft flaky things 
which reflect the light brilliantly, and which can be pulled 
away, or dug out with a knife, in the form of little shining 
plates. The sandstone, on the other hand, is made of 
practically one kind of material throughout, in the form of 
a number of hard and somewhat rounded grains. 

In each case we call these constituents, having characters 
of their own, the minerals which compose the rock. The 
granite consists of at least three distinct minerals, the sand- 



4 OPEN-AIR STUDIES 

stone of only one. Now, if we break up a rock, and select 
a number of fragments of any one kind of mineral, a chemist 
will show us that this mineral is itself made up of certain 
chemical substances, which he can separate and accurately 
determine. He will be able to find out in what proportions 
these chemical substances are present, and will thus give us 
an account of the chemical constitution of the mineral. 

But what about these various substances? They may 
be stated by our friendly chemist to be chemical compounds, 
and these can be further split up into their elements. Or, to 
take the simplest case, our mineral may possibly consist of 
merely one element. 

Here we may remind ourselves of some of our chemical 
notions. We must go back, indeed, to the foundations of 
several sciences for the correct understanding of our rocks, 
and this first chapter is going to be a serious one, before we 
can fairly get out into the country and the open air. But 
we must remember that all the things with which we shall 
deal are quite natural, all come from the earth itself that 
stretches round us ; and those parts of chemistry and physics 
which are possibly a little dull to us seem so merely because 
we cannot handle or directly observe the things about which 
we are being told. If we could see the tiny " atoms " 
moving in the " molecule " of a substance, we should pro- 
bably be as delighted and as fascinated as if we were sitting 
on a mountain-peak and watching the great balance of the 
stars. 

A chemical element is a substance that cannot be split 
up, by any means at present in our power, into any other 
substances with different properties from those by which it 
is itself characterised. It is thus the simplest kind of 
material known to us. Gold, silver, copper, and iron are 
elements; sulphur is an element; so also is carbon, well 
known to us in its commonest form, the " black-lead " of 
our pencils. There are now about seventy elements known, 
and others, at present doubtful, are likely to be added to 
the list. 

The ancients regarded the earth as an element in itself, 
something existing as a foundation for other things, the 
remaining elements being air, fire, and water. What we 
now know as elements were often treated in earlier times 
as varied forms of the same fundamental material ; but all 



THE MATERIALS OF THE EARTH 5 

experiment has shown us up to the present that there are 
really, in this earth and throughout the mighty universe, a 
number of different kinds of matter. To be quite simple in 
our conceptions, we might wish to say that all elements are 
made up of different arrangements of particles of one first- 
formed matter ; but that would be merely guess-work, and 
at present we cannot get beyond our seventy elements. 

If we conceive the smallest particle of an element that 
can independently exist, we may call such a particle an 
atom. It will have a certain weight, and the atoms of 
different elements differ in their weights. But any quantity 
of matter that we can see, even with a microscope, must 
consist of enormous numbers of atoms. 

The atoms are said to be grouped together in molecules, 
or " little masses." Chemists regard the molecule of certain 
elements as consisting of only one atom ; in others, two or 
even six atoms may form the molecule. A molecule has 
been defined by Professor Tilden as " the smallest quantity 
which is able to take part in or result from a chemical 
change." ^ 

A chemical compound is built up of molecules, each of 
which consists of atoms of more than one kind. In the 
simplest compounds the molecule consists of only two 
atoms, one atom of one element being combined with one 
of another. The elements have been shown to combine 
together in fixed proportions, forming compounds with dis- 
tinctive properties. We may hence say that the molecule 
of a compound is the smallest particle into which the sub- 
stance could be divided while yet retaining its peculiar 
chemical constitution. Further splitting might give us cer- 
tain simpler compounds; but ultimately the actual atoms, 
or groups of similar atoms, of each molecule would be set 
free ; in other words, the compound would separate into 
its elements. 

All this may seem beyond human observation ; but large 
quantities of molecules of a compound can be dealt with in 
our experiments, and large quantities of elementary molecules 
can be extracted by chemical processes from them. Or, on 
the other hand, we can cause large quantities of elementary 
molecules of different kinds to combine together to form 
large quantities of molecules of a chemical compound ; and 

^ "Introduction to the Study of Chemical Philosophy," 1876, p. 4. 



6 OPEN-AIR STUDIES 

in either case, by weighing the quantity of each substance 
dealt with, we can find out in what proportions the elements 
are combined in any particular compound. 

We may now glance backwards, and define an atom as the 
smallest quantity of an element that can be driven out of or 
caused to enter into a molecule of a compound in the subtle 
process of destroying or producing any of the known chemical 
combinations of that element. Here we have got down as 
far as we can go in the chemical constitution of a mineral. 
Minerals are made of chemical substances, which are made 
of molecules ; these molecules consist of atoms either (a) of 
different kinds, in which case we are dealing with a com- 
pound, or (b) of only one kind, in which case our substance 
is an element. 

Now we may try to arrive at a definition of a mineral. 
Let us look at those which we have separated from the 
granite — three materials evidently requiring distinct names, 
evidently differing markedly in their physical characters. 

The clear little lumps are called Qimrtz, and do not tell us 
very much by their external appearance. They break across 
witiii irregular curving fractures, much as glass does; and 
they have in this case no regular shape. But they are trans- 
parent, and also very hard; for we cannot scratch them 
with a knife, and they, on the other hand, will scratch glass. 
Moreover, they will not soften and melt, as glass does, when 
held with a pair of forceps in the flame of a Bunsen burner 
— the gas-burner used in chemical laboratories or in ordinary 
gas-stoves. Clearly, they are not grains of glass. 

If we give them to a chemist, he will find in them the two 
elements, Silicon and Oxygen, always in the proportion of one 
atom of silicon to two atoms of oxygen. Quartz is made, in 
fact, of the oxide of silicon, commonly called Silica. We may 
take any of these grains from granite rocks found anywhere 
in the world, and yet their chemical composition will be the 
same. 

The dull white or pink bodies are called Orthoclase, or 
Ortlwclase Felspar ; these, as we have already noticed, have 
the property of breaking across regularly in certain direc- 
tions — in two directions, at any rate — ^when struck with a 
hammer. This shows that their internal structure, the way 
in which the molecules are grouped together, differs from 
that of quartz. Moreover, we can see something of their 



THE MATERIALS OF THE EARTH J 

external shape; it is often regular, and, even on roughly 
broken surfaces of the rock, the larger orthoclases are seen 
to approach the form of small flat bricks. Then, in taming 
about the rock-specimen in the hand, some of these ortho- 
clases seem to be built up of two parts ; that is, one half of 
the orthoclase catches the light and gives a bright reflection, 
while the other half looks dull; clearly the planes of fracture 
are differently sloped in the two parts of the mineral, and it 
has not a peiectly simple internal structure. 

A good knife will just scratch the orthoclase, if drawn 
firmly across it ; but orthoclase will scratch ordinary glass ; 
we thus learn that it is harder than glass, but not so hard as 
quartz. A little splinter of orthoclase can just be melted 
after holding it for some time in the flame of a Bunsen 
gas-burner. 

Our chemist tells us that this mineral is more complex 
than quartz. He finds in it Silicon, Oxygen, Aluminium, 
Potassium, and generally Sodium. The proportion of these 
elements to one another is always the same, except in the 
case of the two last named. Sometimes there is only potas- 
sium present, and no sodium ; sometimes sodium occurs, and 
then there is less potassium. We say that the potassium may 
be replaced in part by sodium without the principal charac- 
teristics of the mineral being altered. In such cases it must 
be a matter of general consent and judgment as to whether 
we are to call the mineral by a new name when such a re- 
placement occurs. The atoms of sodium are lighter than 
those of potassium ; but any difference in the weight of a 
given bulk of orthoclase, according as it contains potassium, 
or both potassium and sodium, would be very trifling. Oases 
often occur, moreover, where a lighter element replaces a 
heavier one, and yet the resulting variety of the mineral is 
actually heavier than the ordinary form. The molecules con- 
taining the lighter element must in such cases lie closer 
together, i.e., there must be more of them in a given space, 
than occurs when only molecules containing the heavier 
element are present. 

So we may note that the chemical composition of some 
minerals may vary slightly, varieties being set up which are 
grouped together under the common mineral name. A mole- 
cule of our typical orthoclase contains 2 atoms of potassium, 
2 of aluminium, 6 of silicon, and i6 of oxygen. But in most 




8 OPEN-AIR STUDIES 

specimens of orthoclase there are some molecules in which 
two atoms of sodium take the place of the two atoms of potas- 
sium. When such molecules are shown by a chemical analysis 
to be numerous, we call the mineral variety Soda-Orthoclase. 

Our third mineral in the granite is called Mica — the plate- 
like substance which is easily dug out with the knife, and 
which gives such a shining appearance to many specimens of 
the rock. Some micas are pale and silvery ; others are quite 
dark, being bronze-coloured or black ; but they have many 
characters in common. Again and again their proper form 
can be seen ; their molecules are clearly capable of building 
up six-sided plates. This structure is so common that it can- 
not be accidental ; and careful measures show that the angles 
of the hexagonal figure are kept the same in the same chemical 
variety. Such a structure is called a crystal ; and a little 
observation will show us that the orthoclase also is in the 
form of crystals, though they have probably not been able to 
grow to such perfection. The mica splits very easily in one 
direction, so that we can flake off thin flexible plates ; and 
even the blacker micas are no longer opaque when one of their 
thin plates is held up to the light. The mineral is quite soft, 
and can often be scratched by the thumb-nail. 

The chemical composition of the micas is still more 
complex than that of the orthoclase felspar, but all common 
varieties contain Silicon, Oxygen, Aluminium, Potassium, 
Magnesium, Iron, and Hydrogen. The pale varieties con- 
tain little iron and usually little magnesium ; the dark 
varieties are richer in these elements and poorer in silicon 
and aluminium. There may be a good deal of replacement 
of one element by another in the mica series, the general 
external characters being retained ; and several different 
kinds or species of mica are recognised, and are known by 
distinct mineral names. 

If we are so fortunate as to find a granite with a number 
of small hollows in it, perhaps half-an-inch or an inch across, 
such as occur in the famous rocks of the northern part of 
the Mourne Mountains, then we may see that all the 
minerals which we have discussed are capable of forming 
crystals, wherever freedom is given to them and when they 
are not too much squeezed together. In such hollows we 
d the mica, and the orthoclase, and the quartz itself, 
itely crystallised, beautifully and regularly shaped, so 



THE MATERIALS OF THE EARTH 9 

that persons looking at the handsome crystals in public 
collections often think that they have been artificially cut 
and polished. But you have only to go into the hills, and 
search in cracks and hollows for yourselves, to find that 
crystals occur naturally, and that they are, indeed, the form 
frequently adopted by natural chemical substances. And, 
further, the crystals of one compound usually differ from 
those of another ; the sides make different angles one with 
another, even if the forms are very much alike; so that, 
by careful observation and measurement of the angles in 
various crystals, we can use the outer shape to help us in 
determining the nature of the mineral. 

And now we can at last arrive at our definition. A 

mineral is a natural substance, formed without the action of 

plants or animals. Its chemical composition is constant, or 

vai^ only by a well-defined series of chxmical replacements. 

Under favourable conditions, it assumes a ci-ystalline form. 

One mineral is known from another by a number of 
characters which must be considered all together; and 
these will be found stated in any text-book of mineralogy.^ 
Let us run over the most important of these characters 
here. 

I. Colour. — When there are several minerals in a rock, 
this character often clearly marks out one from another. 
But it is of far less importance than might be supposed, 
since many common minerals are coloured by some trifling 
impurity ; a sort of stain runs through them, as it were, 
and in their pure condition they are colourless. Metallic 
ores, however, usually have characteristic colours ; thus Iron 
Pyrites, the common iron sulphide, is brass-yellow, and 
Native Copper, the natural element, is copper-red. But, on 
the other hand, the red gem Ruby and the blue Sapphire are 
mere varieties of the same mineral species. Corundum, the 
composition of both being aluminium oxide coloured by a 
substance very insignificant in amount.^ Hence we must 

^ Such as Hatch, ** Mineralogy" (Whittaker & Co.) ; Rutley, "Mineralogy'* 
(T. Murby). 

'^ Artificial corundum has been coloured red (ruby) by adding chromium 
fluoride to the materials employed ; and, curiously enough, the addition of 
this same substance in varying proportions has given rise to sapphires and to 
a green variety. Rubies have also been made by adding potassium bichro- 
mate, and sapphires by adding cobalt oxide (Fouqud and Ldvy, Synthase 
des MiiUraux et des Jtocfies, pp. 220 and 222). 



'^ OPRN-AIR STUDIES 

r«Iy oil oilu^r olmmcteni besides colour in the determining 
of u luiiKU'ul HpooioH. 

2. Transparenoy or Opacity. — Some minerals are 
olmruotoriMtioftlly transparent — in thin flakes, at any rate, 
llwro, again, impiiritios, and chemical changes as the mineral 
altei'H or dt^cays, may rendor a clear substance finally opaque. 
Oaloitt^ (calcium carlwnate) is typically transparent; Iron 
l^rites is opaipie, even when ground down thinner than a 
sheet of notepaper. 

3. Lustre. — Some minerals reflect light brilliantly, like 
Quartz and Rock-Salt, whidi are said to have a "glassy 
lustre," because of tlieir resemblance in this respect to glass. 
Others, as Iron Pyrites, look like polished metal, and are 
said to have a "metallic lustre." Others are quite dull and 
earthy, like Wad, one of the hydrous manganese oxides. 

4. Malleability and Brittleness. — Some minerals can 
be hammered out without breaking, and are said to be 
"malleable," as Native Gold. Others are brittle, and fly 
to pieces when struck, as Iron Pyrites or Quartz. 

5. Hardness. — This is one of the most important and 
useful characters. A mineral may be brittle, and yet may 
be soft enough to be cut into with a knife, like Copper 
Pyrites (sulphide of copper and iron) ; or it may be brittle, 
and yet too hard to be scratched with a knife, like Iron 
Pyrites. For our present purposes, we may note three kinds 
of hardness among minerals : — 

a. Some minerals cannot be scratched by a good knife. 
I. Some minerals can be scratched by a knife, but not 

by the thumb-nail, 
c. Some minerals can be scratched by the thumb-nail. 

Sometimes, in examining our rocks, it is difficult to 

say if some small projecting grain is hard or soft; we 

cannot determine whether we can scratch it, for fear of 

demolishing it or removing it altogether. In such cases 

we may draw it across the side of the knife-blade or across 

our thumb-nail, and see if it scratches either of these, in 

which case it is harder than the substance scratched. If 

the mineral is in the form of loose grains, like those broken 

pftajjB a sandstone, they can be stuck on to a piece of wood by 

^H0rm cement, such as the old bicycle-tyre cement, with 

^bharp little points sticking out above the surface ; and 



THE MATERIALS OF THE EARTH II 

then, held by this handle, we can draw them across the 
knife or across the thumb-nail. Another plan is to squeeze 
them between two plates of glass, such as the slips used for 
mounting microscopic objects ; it is easy then to see whether 
the little grains are scratching the surface of the glass. 

6. Streak. — The colour of the powder of a mineral, 
produced by cutting into it or by crushing it out under 
a clean hammer upon white paper, is called its "streak." 
Every time that we use an ordinary pencil we see the 
streak of Graphite (one form of carbon), the mineral known 
popularly as " black-lead." 

7. Flexibility. — Some minerals can be bent, especially 
in thin flakes, and remain in the form thus given to them. 
They are then said to be "flexible." 

8. Elasticity. — Other minerals are said to be " elastic," 
when, like Mica, they spring back into their former shape 
after being bent. 

9. Specific Gravity. — The statement of the Specific 
Gravity of a substance expresses its relative weight as com- 
pared with pure water at a temperature — in most English 
experiments — of 60° F. If we say that a mineral has a 
specific gravity of 3, we mean that any given bulk of it 
is three times as heavy as an equal bulk of water at 
60° F. A cubic inch of it would thus weigh as much as 
three cubic inches of water at that temperature. Most 
minerals of common occurrence have a specific gravity be- 
tween 2 and 3.5. Meerschaum, used for the bowls of pipes, 
is as low as 1.5, while Gold is as high as 19.3, and a native 
alloy of Platinum and Iridium actually reaches 23. 

In the beautiful system of weights and measures in- 
vented in France, and now used by almost all civilised 
peoples, the specific gravity of a mineral or a rock at once 
tells us how much space a given weight of it will occupy, 
or, on the other hand, how much a given bulk of it will 
weigh. In this system the weight known as I gramme is the 
weight of a bulk of water occupying i cubic centimetre at a 
temperature of 4° C. Hence, adopting this temperature for 
the experiments, i gramme of a substance of a specific 
gravity of 5 will occupy i-5th of a cubic centimetre, or 200 
cubic millimetres, and 100 grammes of it will occupy 20 
cubic centimetres. On the other hand, to take another 
example, 700 cubic centimetres of a mineral with a specific 




12 OPEN-AIR STUDIES 

gravity of 2.5 will weigh 700 X 2.5, or 1750 grammes. This 
is only one example of the admirable convenience of the 
" metric " system of weights and measures, when compared 
with the cumbrous and old-fashioned systems which English- 
speaking children have unfortunately still to learn. ^ 

10. External Form. — In rocks so many causes tend to 
prevent a mineral from getting a fair chance of assuming a 
crystalline form, that the outer shape is of small importance 
compared with many other characters. But to the mineralo- 
gist it is a great means of distinguishing mineral species, 
and the forms observed are grouped in six " systems " accord- 
ing to their greater or less degree of symmetry. The smooth 
surfaces of unbroken crystals, making definite angles one 
with another, are called their /aces, and the number of these 
faces, and their relations to one another, show the degree of 
symmetry of the crystal. 

If you cut an exact square out of paper, you will find 
that it is a highly symmetrical form ; i.e., you can cut it 
across in four directions so that the two pieces produced are 
equal and of the same shape, covering one another exactly 
when the one piece is turned over so as to lie upon the other. 
Then, if you cut out two equal squares, and stand them up- 
right in such a position that a line joining their centres is 
at right angles to both of them, you have a still more sym- 
metrical arrangement formed by two "faces'' of a possible 
crystal ; a pin may be run through the centres of the squares 
so as to hold them in this position. Now make the distance 
between the squares equal to the length of one of their 
sides, and close in the figure by four other squares of the 
same size; we now have a cube, bounded by six similar 
faces. This is a solid figure — it represents a common natural 
crystal-form — which is of the highest known degree of 
crystal symmetry. You can carve nine such forms out of 
some soft stuff, say a potato, and place them side by side ; 
each one may now be cut throngh in a different di/ection, 
so that in each case two halves result precisely similar to 
one another, being merely reversed in position with re- 
gard to the centre of the cube. The surface of division 
between the two halves is in each case called a plane of 

^ For an account of simple apparatus for determiniug specific gravity, and 
for measuring the angles of crystals, &c., see ''Aids in Practical Geology" 
(Griffin & Co.), pp. 13-30. 



THE MATERIALS OF THE EARTH 1 3 

symmetry ; the half on one side of it is, as it were, an exact 
reflection of that upon the other. Hence we say that the 
cube has nine planes of symmetry. A plane of symmetry 
must always pass through the centre of the crystal. 

The six systems under which crystals are arranged have 
received names which need not be explained here, but which 
may be stated for ready reference. They are : — 

I. The Cvinc system, with 9 planes of symmetry. 
II. The Hexagoruxl system, with 7 planes of symmetry. 

III. The Tetragonal^ with 5 planes of symmetry. 

IV. The RhorMc, with 3 planes of symmetry. 
V. The MonodiniCf witn i plane of symmetry. 

VI. The Tridinic, with no plane of symmetry. 

A Triclinic crystal, then, cannot be cut in any direction 
so as to produce two symmetrical evenly balanced halves. 

The symmetiy of natural crystals is often spoilt by certain 
faces growing larger than the corresponding ones on the 
other side of what ought to be a plane of symmetry ; but 
mineralogists discover what the symmetry properly should 
have been by measuring the angles between the faces and 
noting how they repeat themselves exactly in certain sets 
all round the crystal. 

The description of crystals is outside the range of this 
little book ; when we have become interested in observing 
their various forms in nature, we shall some day want to 
turn to one of the simple works on mineralogy for further 
guidance. At present I have tried to give some slight idea as to 
why we say a mineral crystallises in such-and-such a system. 

The same chemical substance sometimes crystallises in 
two, or rarely in three, systems. In such cases we have two 
or even three mineral species, the chemical composition of 
which is identical, but which differ in hardness and specific 
gravity, and perhaps in other physical characters, as well as 
in outward form. 

II. Twinning. — Some crystals are built up of two or 
more parts placed in a singular relation one to another. If 
you take two bricks out of a child's toy-box, and paint one 
of the flat sides of each red, and stand the two bricks up on 
end parallel to one another, their red sides facing in the same 
direction, they may be regarded as two crystals standing in 
similar positions. If we stick the two together, with the red 
side of one touching the plain side of the other, we have 



14 OPEN-AIR STUDIES 

merely, as it were, made a crystal of twice the bulk of each of 
the original separate ones. But if we turn one brick round, 
either on the end on which it is standing, or else, by lifting 
it, turning its lower end upwards, and setting it down again, 
then the two red sides either face one another or face away 
from one another. Stick the two red faces or the two plain 
faces together, and we produce a form in which the two 
halves are reversed in position, and one must be turned back 
again through i8o° before it corresponds in position with 
the other. The parts of some crystals are related in this 
curious way to one another, and such compound forms are 
called " twin-crystals." It is as if the original crystal had 
been cut through the centre, and one half had been turned 
through an angle of 180'' and then stuck against the other 
half again. This may take place several times in one crystal, 
the molecules in one layer building up a structure which 
differs in position by 180° from that in the adjoining layer. 
Orthoclase felspar, which we have already seen in the granite 
(p. 7), is thus simply " twinned," and the two halves catch 
the light diflFerently, because the internal structures are not 
parallel in them; other species of felspar are repeatedly 
twinned, with perhaps twenty layers in a thickness of a 
millimetre. 

12. Cleavage. — In examining the felspar and mica of 
a granite rock, we saw how these minerals broke regularly, 
how they split by preference along certain regular planes. 
Such minerals are said to be "cleaved," or to have a 
"cleavage." Planes of weakness run through them, which 
are found to be related to the crystalline form when this 
also is developed. These " cleavage-planes " are, in fact, 
always parallel to some plane that might occur on some 
possible crystal of the mineral. Again and again we know 
by the occurrence of cleavage that we are dealing with a 
crystalline mineral, one in which the molecules are duly 
arranged, even though the outer form was never perfected 
or has been worn down and rubbed away. 

Some minerals, like Calcite, have three perfect sets of 
cleavage-planes, and can hardly be broken except along 
these planes, every tiny fragment coming away like a little 
independent six-sided crystal. Other minerals, like Quartz, 
are known by the absence of cleavage, and consequently by 
breaking in any direction with an irregular curving fracture. 



THE MATERIALS OF THE EARTH I 5 

13. Magnetism. — A few minerals can be attracted by a 
magnet when finely enoagh broken into powder. Magnetite 
(one of the iron oxides) and Pyrrhotine (an iron sulphide) 
attract particles of their own powder. 

14. Chemical Composition.— This all-important char- 
acter is here placed last, owing to the special and often 
laborious tests required for its correct observation. Many 
minerals cannot be distinguished by a mere qualitative exa- 
mination, but we must ascertain the exact proportions in 
which their constituents are present before we can assign 
them to their proper species. However, with good refer- 
ence-books to hand, a few simple tests for particular 
chemical elements, combined with the observation of the 
physical characters of the mineral, will commonly give us 
the clue without a complete quantitative analysis. Unfor- 
tunately, the silicates are among the most abundant sub- 
stances in the earth's crust, and the minerals formed from 
them are by far the most difficult to analyse. The elements 
combined with the silicon yield their characteristic reactions 
much more feebly than when combined only with oxygen, 
with chlorine, or with sulphur ; most mineral silicates, in 
fact, resist simple attempts to split them up, and yet the 
proportions of their constituents are a fundamental matter 
in the determination of their exact species. 

Now that we know the prominent characters of a mineral, 
we may proceed to define a rock. A Rock is a natural aggre- 
gation of mineral particles, either of one or of different kinds. 
The particles may be in the form of crystals, closely fitted 
into one another; or one of the minerals may serve as a 
cement to unite the whole together ; or the mineral particles 
may lie loosely together, as in sand. Sometimes, but rarely, 
the materials have not separated out into distinct minerals, 
but have remained as a natural glass, all melted together 
and uncrystallised. 

If we search through the rocks known to us from all 
quarters of the globe, we shall soon find that the earth's 
crust is formed mainly of a few minerals repeated over 
and over again. Specimens showing most of the essential 
characters of these minerals can be obtained from any 
geological dealer ; and they will serve as a reference-series 
with which to compare the specimens that we may collect 




1 6 OPEN-AIR STUDIES 

for ourselves in the open air. We will now mn over the list 
of the minerals that are most important for our present 
observations. 

No elementary substance, not even carbon in the form 
of Graphite, can be set down as a common rock-forming 
mineral. We will begin, then, with the simplest compounds, 
the oxides. 

L Oxides, 

Quartz. — Silicon oxide (silica). Colourless. Transparent 
to milky ; glassy lustre. Harder than the knife. Specific 
gravity 2.65. Hexagonal system of crystallisation ; com- 
monly known in small grains, or as duller and more milky 
masses filling cracks in rocks ; crystallises in hollows, &c., as 
six-sided prisms capped by pyramids, which also have six 
sides. No cleavage. One of the very commonest minerals. 
Sandstone is formed of grains of quartz. 

OpaL — Uncrystallised silica, partly hydrous. Glassy and 
transparent. The variety used as a gem is coloured by the 
occurrence of minute flaws in it. Unscratched by knife. 
Specific gravity 2.25. Common in the mixture called Chal- 
cedony, or, when less pure, Flint, which is formed of finely 
mingled quartz and opal. Chalcedony and Flint occur in 
cracks, and as lumps and nodules in limestone rocks, and 
are easily known by their hardness. 

Magnetite. — Iron oxide, each molecule containing 3 
atoms of iron to 4 of oxygen. Black and opaque. Lustre 
somewhat like that of the black-lead in a pencil. Harder 
than knife. Specific gravity 5. Cubic system, crystallising 
in little double pyramids, the faces of which are eight equi- 
lateral triangles. Easily attracted by magnet, and attracts 
iron filings, as well as its own powder. Occurs often as 
tiny grains scattered through a rock. 

I^QlOllite. — Hydrous iron oxide, the molecule containing 
6 atoms of hydrogen, 4 of iron, and 9 of oxygen. Warm 
yellow-brown; opaque and usually dull. Sometimes quite 
soft and powdery. Streak yellow-brown. Crystalline form 
unknown. This mineral consists of common iron rust, and 
forms most of the brown stains in rocks, resulting as it does 
from the decomposition and alteration of minerals contain- 
ing iron. Magnetite is often coloured brown by this action 
on its exterior. 



THE MATERIALS OF THE EARTH 1 7 

II. Cklorides. 

Rock-Salt. — Sodium chloride. Colourless, unless tinged 
with an impurity, such as limonite; transparent; lustre 
glassy on good surfaces. Easily scratched by the knife, 
and even by the thumb-nail. Cubic system, forming cubes. 
Soluble in water, and easily known by its taste. 

III. Sulphides, 

Iron Pyrites. — Iron sulphide, with 2 atoms of sulphur 
to I of iron. Brass-yellow and opaque; metallic lustre. 
Not scratched by knife. Specific gravity nearly 5. There 
are two species included under this name: one, called 
Pyrite, crystallises in the cubic system, often forming neat 
little cubes, and being well seen in slaty rocks ; the other, 
Marcasite, is rhombic, and commonly occurs as a replace- 
ment, or forming casts, of fossils, so that we see shells, and 
even fishes' teeth and spines, preserved in this bright brassy 
material. Marcasite, however, decomposes rapidly, giving 
oflF fluflFy white products ; while Pyrite can be easily kept in 
collections. Pyrite alters slowly in nature, where exposed, 
into soft brown powdery limonite. 

IV. Carbonates, 

Calcite. — Calcium carbonate (i atom of calcium, i of 
carbon, and 3 of oxygen in each molecule). Colourless and 
transparent. Lustre almost glassy. Easily scratched by 
knife, and thus at once distinguished from quartz. Specific 
gravity 2.72. Hexagonal system, forms very various; but 
all break up along three perfect series of cleavage-planes 
when struck. Calcite is a very common mineral, forming 
the rocks called LiTnestone and Marble, in which it is often 
coloured by impurities. When a drop of acid, such as 
hydrochloric or sulphuric acid, or strong vinegar, is placed 
on calcite, the mineral begins to dissolve, freely giving off 
bubbles of carbon dioxide gas. 

Aragonite. — Same composition as calcite, but rhombic 
in crystallisation. General characters similar, but specific 
gravity 2.93. Rarer than calcite ; but many sea-shells are 



l8 OPEN- AIR STUDIES 

made of aragonite, while others are made of calcite. Be- 
haves like calcite with acids. 

Dolomite. — Calcium carbonate and magnesium carbonate 
in equal proportions, forming a compound carbonate. The 
constituent elements are thus calcium, magnesium, carbon, 
and oxygen. Generally resembles calcite, even in cleavage, 
but specific gravity 2.85. Hexagonal system. Does not 
give off bubbles of gas in acid unless the liquid is heated. 

ChaJybite. — Iron carbonate. Faintly brown ; lustre 
almost glassy. Generally resembles calcite, even in cleavage, 
but specific gravity nearly 4. Hexagonal system. Often 
occurs imperfectly crystallised, forming great nodules and 
lumps in clays, and often surrounding fossils. 

V. Sulphates, 

Gypsum. — Hydrous calcium sulphate, each molecule 
containing 4 atoms of hydrogen, I of calcium, i of sulphur, 
and 6 of oxygen. Colourless and transparent ; glassy 
lustre. Scratched by thumb-nail, and thus at once dis- 
tinguished from calcite. Flexible in thin plates. Specific 
gravity only 2.3. Monoclinic system, often forming some- 
what flat crystals; often, however, fibrous. One cleavage 
very conspicuous. Occurs in clays, as detached crystals and 
as plates and veins ; when present in considerable quantity, 
forms the rock known as Alabaster, 

VI. Silicates, 

First we may take three of the group known as the 
" Felspars." 

Orthoclase Felspar. — Potassium aluminium silicate, 
usually with some sodium, as we have already mentioned 
farther back (p. 7), when we were considering the chemical 
composition of minerals in general. Colourless, with glassy 
lustre, when quite unaltered, but commonly duller white or 
pink. Just scratched by a good knife. Specific gravity 
2.56. Monoclinic system, usually in forms somewhat flattened 
in one direction. Crystals almost always simply twinned, 
as can be seen upon broken surfaces. Two perfect cleavages, 
at right angles to one another, whence the name Orthoclase. 

Albite Felspar. — Composition similar to orthoclase, but 
sodium entirely takes the place of the potassium. In 



THE MATERIALS OF THE EARTH 1 9 

general appearance like orthoclase, but only rarely of a 
pink colour. Just scratched by knife. Specific gravity 2.6. 
Triclinic system ; repeatedly twinned, so that the crystals 
are built up of delicate alternating layers. Two good 
cleavages, which are not exactly at right angles. 

Anorthite Felspar. — Calcium aluminium silicate, the 
molecule containing i atom of calcium, 2 atoms of 
aluminium, 2 of silicon, and 8 of oxygen. Resembles 
the other felspars in appearance ; commonly dull white. 
Just scratched by knife. Specific gravity 2.72. Triclinic 
system ; repeatedly twinned. 

The species of felspar form a closely connected series, 
Oligoclase, sodium calcium aluminium silicate, and 
Labradorite, calcium sodium aluminium silicate, being 
forms intermediate in composition between albite and anor- 
thite, and also crystallising in the triclinic system ; the 
former contains more sodium than calcium, and the latter 
more calcium than sodium. These very common minerals, 
the felspars, provide us, as we shall see, with important 
products when they decay away. All the felspars except 
orthoclase, being triclinic, have their two chief cleavages 
not perpendicular to one another, and are classed together 
as " slanting-cleaved " or Plagioclase felspars. 

Next comes a group of minerals rich in magnesium and 
iron. 

There is one series known as the Amphiholes, from 
which we may select the common species Hornblende. 
This is a complex silicate of magnesium, iron, aluminium, 
and usually some calcium. Colour dark green, dark brown, 
or black ; glassy lustre when fresh. Scratched by knife, 
but not easily. Specific gravity 3. Monoclinic system; 
often occurs as long prisms and fibrous groups. Two fair 
cleavages at about 120" (precisely 124° 30') to one another. 

Prom another important series, the Pyroxenes^ some of 
which are monoclinic and some rhombic, we may choose 
Angite. In composition this mineral may be identical with 
hornblende ; it is similarly dark in colour, is just scratched 
by the knife, has a specific gravity of 3, and is monoclinic. 
But it typically forms shorter prisms, and the angles between 
the faces of the crystals differ from those of hornblende. 
The two cleavages similarly differ, being practically at 90° 
(precisely 92° 55') instead of at about 120°. Hornblende 



^^ OPEN-AIR STUDIES 

and augite are interesting examples of how the same sub- 
stance may assume, under different conditions of growth, a 
distinct set of crystal forms. If hornblende is melted up and 
made to crystallise again on cooling, the forms produced are 
those of augite. On the other hand, in rocks a slow natural 
change goes on, by which the molecules in crystals of augite 
rearrange themselves and produce crystals of hornblende. 
Hornblende thus seems to be the more lasting and settled 
and steady-going form to which these molecules give rise, 
borne pyroxenes, closely allied to augite, contain soda mole- 
cules, and may be styled soda-pyroxenes. The rhombic 
pyroxenes do not contain alumina, being silicates of mag- 
nesium and iron, with about 50 per cent, of silica. 

. ^*jVUie. — Magnesium iron siKcate, without aluminium, and 
with less silica than the pyroxenes and amphiboles. Yellow- 
8^®^ ^^ brownish yellow ; transparent, with glassy lustre, 
when fresh, but decomposes readily to dull brown and deep 
black-green patches. Not scratched by knife when fresh, 
but commonly quite soft and altered. Specific gravity 3.3 
when fresh. Rhombic system, but usually occurs merely as 
somewhat rounded grains. Two cleavages often seen, break- 
ing the crystal up into minute brick-like masses. During 
alteration, the mineral takes up water, turns out some of its 
iron atoms, and forms the soft green, black, or reddened 
mineral called Serpentine. Rocks largely composed of 
olivine thus decompose, and form the ornamental serpen- 
tine rocks. 

We have already (p. 8) discussed some of the characters 
of the next minerals, the Mica series. Muscovite Mica is a 
hydrous silicate of potassium, sodium, and aluminium, differ- 
ing from orthoclase by being hydrous, i.e., containing some 
water, and by the silica forming only about 45 instead of 65 
per cent, of the total weight of the mineral. Colourless to 
bronze-brown; transparent in flakes, and used, under the 
trade-name of "talc," for covering gas-globes and lamp- 
chimneys. Silvery lustre. Just scratched by thumb-nail ; 
the knife scratches it very easily, with a characteristic grating 
sound. Specific gravity nearly 3. Monoclinic; commonly 
forms six-sided plates. Perfect cleavage, splitting up the 
■jj^ystals into the most delicate transparent layers. These 
^^■fers are elastic. 
^BSiotite Mica is a hydrous silicate of potassium, aluminium. 



f 

\ 

\ 



THE MATERIALS OF THE EARTH 21 

magnesium, and iron, the proportion by weight of the silica 
being less than in muscovite. Dark bronze, black, or dark 
green ; translucent in thin flakes. Hardness and other ex- 
ternal characters like muscovite. It is sometimes impossible 
to distinguish specimens of muscovite and biotite without 
chemical or microscopic tests. For our purposes in our walks 
abroad, it will be sufficient if we can recognise such a mineral 
as one of the Mica series. 

Chlorite.— Hydrous aluminium magnesium iron silicate. 
Dark green, generally resembling a green mica, but some- 
what duller, and very easily scratched by the thumb-nail. 
This mineral commonly occurs as a product of the slow 
alteration of amphiboles, pyroxenes, and micas, and gives a 
prevalent green tinge to many decomposing rocks. 

Kaolin. — Bjydrous aluminium silicate, the molecule con- 
taining 4 atoms of hydrogen, 2 of aluminium, 2 of silicon, 
and 9 of oxygen. White and powdery, dull in lustre, re- 
sembling flour. Specific gravity about 2.5. Rarely found 
crystallised, when it forms small six-sided plates. Kaolin 
is the common product of the decomposition of potassium 
and sodium felspars and of similar minerals rich in alumi- 
nium ; mixed with iron oxides and animal and vegetable 
stainings, it forms the bulk of all the common rocks called 
Clays, 

We have now enumerated some twenty-six minerals 
which we shall commonly meet with in our observations 
of the earth's crust. One point must have been forced 
upon us in glancing over the descriptions. These common 
minerals consist of only a very small number of the seventy 
known chemical elements. The part played in the earth 
by the rarer elements is possibly of great importance. Small 
additions of them to a mineral may, perhaps, change its 
mode of growth or its whole physical characters and external 
aspect; just as, in making metallic castings, very small 
admixtures of some element may make a world of diflFerence 
in the toughness and hardness of the finished product. 
But, if we have now correctly enumerated the commonest 
minerals of the earth's crust, the bulk of that crust, at 
any rate, must clearly be made up of a limited number of 
constituents. 

Professor Prestwich ^ gives us the following estimate of 

* "Geology," vol. i. p. 10. 



22 



OPEN-AIR STUDIES 



the proportion hy weight in which the elements occur in 
the earth's crust 



Oxygen 

Silicon 

Aluminium 

Calcium 

Magnesium 

Sodium 

Potassium 



Per Cent. 
50.0 
25.0 
1 0.0 

4.5 

3-5 
2.0 

1.6 



Carbon 
Iron 
Sulphur 
Chlorine^ 
Other elements, includ- 
ing Hydrogen 



} 



Per Cent. 



2.4 



I.O 



1 00.0 



We may conceive that the oxygen, which forms half 
the weight of the earth's crust, is distributed among the 
other elements, and we may state the components of the 
crust as oxides, which is the form in which they commonly 
occur when they build up minerals. Thus aluminium 
silicate may be regarded as a combination of silica (silicon 
oxide) and alumina (aluminium oxide). Water, again, is 
an oxide of hydrogen, and calcium carbonate is a combina- 
tion of carbon dioxide and lime (calcium oxide). When 
stated thus, we find that Silica forms 53 per cent, of the 
crust by weight, Alumina 19 per cent.. Lime and Magnesia 
(magnesium oxide) about 6 per cent, each, and Soda (sodium 
oxide) and Potash (potassium oxide) each 2.5 per cent. A 
large amount of the available oxygen is thus bound up with 
silicon, the silica crystallising as quartz, or forming silicates 
by union with the other oxides. Of these common oxides, 
only a few form minerals without further combination : 
these are, firstly, silica ; secondly, the iron oxide in which 
2 atoms of iron are united with 3 of oxygen (which forms 
a deep-red ore called hcematite) ; and, thirdly, water (which 
crystallises in the hexagonal system as ice). The mineral 
magnetite is really produced by the union of two distinct 
oxides of iron, one constituted as above stated, and the other 
consisting of molecules with i atom of iron to I of oxygen. 

When we have thus set our ideas in order, and have got 
our small collection of typical rock-forming minerals together, 
we shall often have hard work in determining the consti- 
tuents of the rocks that we bring in from our country expe- 
ditions. In a coarse-grained granite we can pick out the 
minerals from one another, and see clearly that they are of 
distinct kinds. But in many rocks the mineral particles are 
exceedingly minute, and the whole mass looks at first as if 



THE MATERIALS OF THE EARTH 23 

it were composed of only one kind of material. We may 
overcome this diflSculty by various methods which have been 

devised for separating the constituents of rocks. 

The rock must first be broken up with a hammer, all the 
fine dust and smaller fragments being preserved, together 
with the larger pieces. A great deal can then be done by 
simply throwing the whole material into a shallow pie-dish or 
a soup-plate, and washing well with water. The water is 
poured upon the powdered rock, is well shaken, and is then 
poured oflF again into another dish. It carries with it much 
of the finer material, and this can be entirely removed if the 
operation is again and again repeated. Soon we have re- 
maining in our original dish only the coarser and less useful 
fragments, and we can give our attention to the second dish. 

Here it may be worth while to make a further separation, 
and to wash oflF the very finest material into a third dish. 
Our object will be to produce a material in which the par- 
ticles are so small that each consists practically of only one 
kind of mineral. We must examine the product from time 
to time with a hand-lens, until we can see the lighter and 
darker constituents lying cleanly side by side. Then we can 
take a small quantity of this material — say, enough to cover a 
sixpence — and dry it gently on a clean piece of brass or iron 
over a lamp or candle. The iron may be held with a pair of 
pliers during the gentle heating. 

When dry the particles will roll about freely, and any 
specially desirable ones can be picked out from the rest. 
A moist colour-brush is good for this purpose, the lens 
being held in one hand and the brush in the other. The 
brush is dipped in water and a fine point is given to it ; any 
of the little grains stick to it when touched, and can be 
deposited in some safe vessel for examination. The common 
circular earthenware palettes of children's colour-boxes are 
good receptacles for the minerals during sorting. 

When we have thus extracted a number of examples of 
the minerals that look different from one another, rejecting 
all grains that are composed of more than one mineral, we 
can test these materials in various ways. Their hardness 
can be found by sticking them on to a handle of wood as 
suggested on p. 10, and drawing a knife, or other minerals 
of known hardness, or the thumb-nail, across them. Eefined 
but easily applied methods have been invented for determin- 



I 



I 



24 OPEN-AIR STUDIES 



11 



ing even the specific gravity of minute grains.^ Chemical 

tests can also be brought to bear. A drop of hydrochloric 

acid, or other chemical reagent, can be placed upon an 

isolated mineral grain, which is suitably supported on a 

square of glass, and the resulting action or absence of action 1 1 

can be examined with a lens or a microscope. 

The microscope was used by the French observer, Cordier, 
in 1815^ for the determination of tiny mineral specimens 
such as these; and he compared his particles with those 
obtained by powdering up known minerals. In this way 
he proved that some rocks, which were supposed to be of 
uniform constitution throughout, were in reality composed 
of several distinct minerals, held together, in some cases, 
by uncrystallised glassy material lying between their grains. 

Cordier used sieves of various degrees of fineness, through 
which to sift the powdered materials. This forms one of the 
very best means of separation; but the production of a 
suitably fine sample by mere washing is quite practicable, 
and is so simple that any one can attempt it with ordinary 
household-apparatus. But the work must be done near a 
sink, or in some place where no one will object to the 
splashing of a little water. 

Magnetite, and fragments in which even a small propor- 
tion of magnetite occurs, can be picked out from powdered 
rocks by merely passing a dry magnet over the powder. 
The magnet must be in no way damp, or grains of the other 
minerals will stick to it. 

When it is necessary to know how the minerals in a 
rock are related to one another, and what their exact arrange- 
ment is in the mass, a flat surface can be produced on part 
of the rock-specimen by grinding ; it can then be polished, 
and can be inspected with the lens or microscope. Thus 
the various mineral constituents may usually be clearly seen 
in place. The grinding-down can be done most conveniently 
by getting a piece of lead about six or seven inches square 
and strewing emery upon it. Emery of suitable fineness is 
called "90-hole," since it is sifted through a sieve with 
90 holes to an inch, or 8100 to the square inch. Emery 
can be bought cheaply from an oil-and-colour merchant or 
an ironmonger. The emery powder is scattered on the lead 

^ See " Aids in Practical Greology," p. 28. 

^ Journal de Physique^ tome Ixxxiii. (1816), pp. 135, 285, and 352. 



THE MATERIALS OF THE EARTH • 2$ 

plate, and is made into a thin paste with water ; then a 
small lump of the rock is held in the hand and is rubbed 
about on the plate with a circular motion, being all the time 
pressed firmly down. Water must be added from time to 
time. When a fairly smooth surface has been produced, 
the specimen should be washed and further ground down 
upon a square of plate-glass, cut from the "remainders" 
of a glazier's yard; on this glass a finer emery known as 
" flour-emery " should be scattered. Plenty of wat^r must 
be used. The specimen is again washed, and the surface 
may -often be examined successfully in a wet state under 
the microscope, appearing then as if polished. Or it may 
be varnished over, which serves the same purpose in pro- 
ducing a good smooth surface. Or it may be fairly polished 
by rubbing briskly on an old worn carpet, the dust in this 
helping the operation. The rock gets rather hot to hold, by 
reason of the rapid friction, and water cannot now be used ; 
but the brisk work of a very few minutes will produce a 
useful polish. Professional polishing is done with rouge (pow- 
dered haematite) upon a stretched surface of wash-leather. 

Sometimes it is a great advantage to grind a piece of 
the rock so thin that the light shines through it, in which 
state it can be examined as a transparent object under the 
microscope. This is by no means so diflScult as at first appears, 
and any friend accustomed to use the microscope would be 
willing to assist in the final mounting of the specimen. The 
simplest way to prepare rock-sections is as follows : — 

1. Choose a fragment of the rock, as flake-like and as thin 
as possible, and about an inch across, and grind down one 
surface with emery. 

2. Finish this surface carefully by rubbing, with plenty of 
water, on a Water-of-Ayr hone, to be obtained of any good 
tool-shop. 

3. Get some ordinary glass slips for mounting microscopic 
objects, measuring three inches by one inch ; dry the rock- 
flake, and cement its smooth surface to one of these with 
stiflF Canada balsam (procurable from a chemist). Heat the 
slip gently on a piece of metal supported over a lamp, until 
the balsam slowly gives up the spirit in it, and remains liquid 
only by reason of the high temperature. This stage can be 
judged of by dipping the end of a wooden match from time 
to time into the balsam round the specimen. The balsam 



26 OPEN-AIR STUDIES 

brought away cools quickly in the air, and when it is seen to 
become brittle on cooling the operation has gone far enough. 

4. Then press the specimen firmly down upon the glass 
slip, to drive out any bubbles under it ; remove it from the 
lamp and let it slowly cool. 

5. Now, using the glass as a handle, grind down the re- 
maining rough surface of the rock. In this way the speci- 
men will gradually become possessed of two parallel surfaces ; 
it will become thinner and thinner, until light begins to be 
visible through it; and it must be finished on the flour- 
emery, and finally on the hone. With care, all parts of it 
can be made equally thin, and it may then be washed well 
and allowed to dry. 

6. Cover the thin section thus made with Canada balsam, 
and place on this a thin cover-glass, such as microscopists ordi- 
narily use. Dry the balsam slowly as before, being very careful 
to avoid overheating and the consequent production of bubbles. 

7. The section will now be ready for the microscope. Any 
balsam that has oozed out upon or round the cover-glass can 
be lightly cleaned oflF with a cloth dipped in spirits of wine. 

For casual examination, the finished section need not be 
covered, but may merely be moistened with water, and can 
thus be examined under the microscope. 

A good rock to begin upon is a fairly hard chalk, a sub- 
stance which grinds down easily and which is yet permeated 
by the balsam and rendered coherent. Sections of chalk 
can be prepared entirely on the Water-of-Ayr stone. 

So much for indoor considerations and observations. In 
our walks abroad we must carry two instruments, a hammer 
and a pocket-lens. The hammer may weigh about a pound, 
and its head should have a good chisel-like edge on one side 
and a square steel face on the other. The chisel-edge is best 
placed perpendicularly to the direction of the handle of the 
hammer. 

A small stone-mason's chisel is always worth carrying, and 
even a light hammer and a chisel combined will often do 
what a heavier hammer alone could not eflFect. Large blocks 
of stone can be wedged out by steadily driving the chisel 
into some natural crack. 

The best pocket-lens for our purpose is the common 
" triplet," with three lenses of different power folding up into 
one cover. 



THE MATERIALS OF THE EARTH 27 

And now we can at last set off on our travels. We have 
taken pains to learn something of the alphabet of our sub- 
ject ; and any one of us may hope in time to apply these 
studies to the actual examination of the earth. In our own 
immediate surroundings — even in the muddy rivers that run 
through great cities — there is something to be observed, 
something far more important and interesting than anything 
which we can learn by the mere reading of books indoors. 
If I describe in these pages the details of some landscape 
that is familiar to myself, or bring together for illustration 
the features of several landscapes, it is with the hope of 
encouraging each reader to make similar and better observa- 
tions in his outdoor wanderings for himself. It is well to 
note down our impressions, making little sketches, however 
rough, of what we see — the form of a boulder, the series of 
rocks exposed in a quarry, the outline of a hillock or of a 
mountain-range. Until we put our notes on paper, trying 
to be as exact as possible, we really do not know how many 
things we may notice in a short day's ramble ; and, when we 
have written them down, we constantly require to go back 
again to fill in some gap in our observations. And even 
then we feel a desire to fit things together, so as to explain 
them ; whereupon we shall find that a single Kf etime and 
our individual wits are quite insufficient for the purpose. 
We must take counsel of various other people ; we must 
examine their books, and what they have extracted out of 
previous centuries of books ; and all the time we must be on 
the look-out, for possibly it may be given to one of us to 
see what no one before has seen exactly in the same way. 
And then we shall have made a geological discovery. 

After all, it matters very little whether the persons who 
have gone over the ground before us have or have not seen 
all that we can see. The delight of thus wandering, with our 
eyes wide open, across the airy moorland or along the shingle 
of the beach, is one that will grow upon us, and that can 
never again be taken away from us or lost. We shall be 
every hour finding out things for ourselves, no longer pent 
up in museums or laboratories, but among the broad ridges 
of the world, seeing how the wind, and the streamlet, and the 
ocean, and the rocks, all work together, witn the great sun 
shining overhead. 



CHAPTEE II 

A MOUNTAIN-HOLLOW 

Now let us come out and see what is happening all round 
us. Every spring we notice how the trees bud forth again ; 
how the tender coils of the ferns begin to push up through 
the dead brown leaves that have coloured the hillsides all the 
winter ; how the primroses look out and shine like stars along 
the green borders of the lane. In the summer we watch the 
com changing, and the fruit reddening on the boughs ; in the 
autumn we notice that the woods are golden, and that the 
leaves soon begin to fly through the air, as if some caliph of the 
Arabian Nights were scattering coins in the sunlight. Then, 
from one year to another, we can see how animals grow up ; 
the little kitten changes, and becomes a quiet old cat that 
loves to sit by the fireside ; the white lambs, which used to 
run up to us inquisitively in the fields, soon alter into thick- 
bodied and uninteresting sheep. All these things grow, and 
go on changing ; but the fields themselves, the broad slopes 
where the heather gathers, the barren rocks above, and the 
long dark ridges of the hills, all these seem to remain, and 
never to grow, or alter, or decay. 

Well, let us set forth on our travels, and keep our eyes 
well open. Perhaps we may find out that the hills are 
changing after all. 

We must imagine that we wake up on a fine clear morn- 
ing at the foot of some of our wild mountain-masses in the 
British Isles — perhaps at the head of Windermere, or in the 
passes around Snowdon, or in Perthshire, along the great 
Highland border, or among the purple slopes of Kerry or 
the barren moors of Donegal. Our little farm-house lodging 
lies by the high-road up the glen ; far away we can see the 
cart-track winding, now crossing some spur above the stream, 
now descending to the valley-floor ; and on either side of it 
a few cottages stand dotted about the lower slopes. Above 

them the steeper moorland rises, grey-green and purple, and 

28 



A MOUNTAIN HOLLOW 29 

crossed here and there by bands of stones or cut into by rush- 
ing little streams. 

We must climb to-day steadily up into the hollows of the 
mountains. We must leave the white cottages far below us ; 
and, as we pass through the last gate in the stone wall, we 
find ourselves on the open moorland. A few grey blocks of 
stone lie half buried in the furze and heather ; there used 
to be many more of them, before the farmers gathered them 
and laid them together to make the walls. Some were so 
large that they had to break them up with gunpowder ; you 
can still see the marks of the boring-tools on them, where 
the holes were made in which the blasting-cartridges were 
placed. 

A little above us, a few huge blocks remain untouched ; 
and one or two are as large as a labourer's cottage. If we 
walk round one of these, we shall very likely find a number 
of smaller stones wedged up against it, as if they had come 
tumbling down the slope aud had been stopped by their 
bigger brother. Every now and then we hear faint sounds 
of water trickling ; it is making its way down among the 
stones that have become quite buried in the grass. I£we 
dig for a little while with a walking-stick, we may be able 
to see the tiny streamlet flowing; or at any rate we can 
stoop down and hear it much more clearly. We see that 
the hillside is partly made of blocks of stone, loosely piled 
on one another ; and the water can find a path between them. 
It washes along earth and sand as it flows downward, and 
sometimes in this way it fills up the spaces between the 
stones, and has then to move away into another course. If 
you put your hand down into the crevices, you will probably 
bring up some of the fine sand. 

How far down does this assemblage of loose blocks ex- 
tend into the hill? Well, let us come across to the big 
stream which here foams down the mountain-side. When 
we were down below, it looked like a white streak ; but, now 
that we stand by it, we find that it is a fair-sized river. The 
banks are twenty feet or so in height, and they show us the 
stuifs of which the ground hereabouts is made. Great blocks 
of stone stick out on the steep sides, heaped together in a 
coarse sand. Down where the stream itself is running, we 
can see the solid rock ; and here and there there are fine 
deep pools, or narrow gorges which look as if they had been 



30 OPEN-AIR STUDIES 

cut out by a mason. So we learn that there is solid rock 
under us, forming the mass of the mountain, covered by 
perhaps twenty feet of the loose gravel with the big stones 
scattered through it. 

What we have seen in the side of the great stream is 
called a section ; it is as if we had cut down into the earth 
for ourselves and had seen the different rocks lying there 
one upon another. A slice of wedding-cake shows, in the 
same way, the sugar, and the almond-layer, and the cake 
itself, ** in section." Every quarry and every railway-cutting 
similarly give us a geological section. 

Now we must move on upwards, although the slopes 
grow steeper ; and there are now plenty of blocks among 
which we have to pick our way. Little cliffs of solid rock 
also stand out above us, and we must climb up by the gullies 
through them, or find a way round to right or left. The 
loose blocks, half buried in the gi-ass, are made of the same 
materials as the cliffs ; here and there we may find a puzzling 
stranger, but the vast majority seem just to have fallen from 
the crags above us. This observation will very soon be use- 
ful, as we reach the higher levels of the mountain. 

If you kick a stone from under you, it goes bounding 
down across the grass, it leaps over one or two of the little 
cliffs, and so descends until it rests on some lower ledge 
of the hillside. Every time that the sheep walk along the 
paths made by them, a few stones become dislodged and 
move farther down into the valley. So that the surface 
of the slope is changing, as surely as the bracken changes 
and dies away in winter; only it might be many, many 
years before we should notice that the whole mountain 
was thus decaying. 

If we follow up the stream itself, we shall see that 
something interesting is going on there. The deep pools 
often occur at the foot of waterfalls, and here the water 
is violently churned up, white and foaming, while it awirls 
away steadily to its outflow at the farther end of the pool. 
If it is a time of flood, we shall see little more than this 
commotion; but during a dry spring or summer we can 
walk out on the exposed rocks right into the middle of the 
stream. In these rocks there are a number of circular 
hollows, sometimes imperfect and open on the side that 
lies farthest up the stream ; some are a foot or more across, 



A MOUNTAIN HOLLOW 3 I 

others are too small to get one's hand into; and in each 
there are one or more ronnded pebbles, and often a good 
deal of fine sand. 

At first it lookB as if these materials had been washed 
down and had falleii naturally into the holes; and this is 
certainly true of most of the smaller stones and Band. Bat 
the holes themselves require explanation, for some of them 
resemble the drill-marks in the stones blasted by the fi 




down below. Their inner surface is beautifully smooth, and 
their depth is often greater than their width ; now and then 
there are a few grooves running round the inside, as if the 
drill for a time had tended to make them rather larger. 

If we choose the simplest case, we find that there is one 
large pebble in the hole, and we can move it round and 
round when we reach down to it with our fingers. The fact 
is, that the pebble has drilled ont the hole in which it lies. 



32 



OPEN-AIR STUDIES 



At some time or other a stone got wedged in one of the 
cracks of the rocky bed of the stream ; the rush of water 
kept turning it round and round, and supplied it with sand, 
which helped it to cut into the rock. Every one knows how 
a grain of hard sand, caught in between, let us say, a 
polishing-cloth and the handle of a bicycle, will cut deeply 
into the metal at every movement of the hand. Thus the 
stone bored its way down, until no force of the stream 
could dislodge it again ; and, every time that the flood 
comes over it, it works away in its little prison, deepens the 
floor of it, and smooths and polishes the sides (fig. i.). 

Such holes are called pot-holes, and may be seen in 
hundreds when the stream is low. If they can be made 
so freely in these ordinary rapids, we can guess what is 
going on under the waterfalls themselves. Several pot- 
holes often cut into one another, and finally form one large 
one ; and in this way, in the swirls of the river, basins are 
finally carved out of the solid rock. This is the history 
of the beautiful deep pools which occur in connexion with 
the falls. 

In Norway, a country famous for its waterfalls, the pot- 
holes have been called " Giants' Kettles." Some of those 
best known to travellers occur in the " Glacier-Garden " of 
Lucerne in Switzerland, one of them being 26 feet wide and 
30 feet deep. 

Mr. H. J. Marten ^ has given us some interesting figures 
as to the rate at which pot-holes can be worked out in soft 
red sandstone, a rock familiar to dwellers in the midland 
countie^^ of England. In 1844 a weir was built at Holt 
Fleet, where the Tenbury and Droitwich road crosses the 
valley of the Severn. In 1 887 it was found that a number 
of the stones on the apron, or the slope of the weir facing 
down the stream, " had been drilled through and through by 
the action of the current upon small pebbles lodged either 
in hollows on their exposed surfaces or between the joints of 
the stones." The Severn, in this steeply banked and pic- 
turesque part of its course, brings over each square foot of 
the apron about 2000 gallons of water every minute, moving 
at a rate of 12 to 15 feet per second ; and the current has 

^ ** On Some Water- Worn and Pebble- Worn Stones taken from the Apron 
of the Holt-Fleet Weir on the River Severn," Quart, Joum. Geol. Soc., vol. 
xlvii ( 1 891) p. 63. 



A MOUNTAIN HOLLOW 33 

been known to move fair-sized boulders up the steep face of 
the weir and to push them over the crest and down the apron. 
Six stones, about 6 feet long, 2 feet broad, and 2 feet 6 inches 
thick, were specially examined by Mr. Marten, and it was 
shown that in forty-three years the eroding action of the 
stream had cut away about half their bulk, and had removed 
two inches of stone from the general surface of the weir. 
Of course the softer portions would go first; but it seems 
likely that in a hundred years these large stones would have 
been entirely destroyed. 

It is now clear that a rushing stream, like that on our 
mountain-side, pushes along any loose . stones that may fall 
into it, and can even move big boulders if the slope of the 
ground is steep enough. The rough stones grind against 
one another, and those of medium size soon have their 
comers knocked off, and finally become rolled into pebbles. 
But a very long journey down stream is required before the 
finer materials become well rounded, and many of the little 
grains of sand, which are easily washed apart from one 
another by the water, come out at the mouth of the river 
practically as sharp as when they fell into the water. A 
good deal of the sand is also produced by the grinding of 
one rock against another, and, as a rule, the smaller the 
fragments thus taken off, the less chance there is of their 
being made into true round pebbles. 

Of course some materials of the earth rapidly go to pieces 
under this rough treatment, and hence the pebbles may not 
fairly represent all the different rocks that have fallen into 
the flowing stream. We may have only the harder and 
more resisting ones remaining, and some materials may be 
broken mechanically into fine powder, while others may 
actually become slowly dissolved away in the water. But 
here on our higher mountain-slopes the stones have not 
travelled far enough for any sorting out of the different 
kinds to have occurred. If there is a limestone or a shaly 
rock above us, we shall still find pieces of it lying in the 
streams, side by side with the hardest rocks, such as those 
composed of quartz. 

If we watch long enough, particularly after rain, we shall 
see these pebbles and small stones actually moving. I 
remember, after a thunder-shower near Thun in Switzerland, 
how the lumps of rock, about the size of cricket-balls, came 



34 OPEN-AIR STUDIES 

rolling down a shallow streamlet as if they were being 
bowled down upon us from above. And we may now go a 
step further, and notice how the constant passage of stones 
and sand over a rock tends to cut a groove in it, just as a 
stone, when kept moving near one point, works out for 
itself a pot-hole. Hence the little gorges, which look like 
rents in the solid rock, have really been cut by the torrent, 
which uses such stone tools as are given to it ; and in this 
highland region they are still being deepened as the waters 
rush down daily. Of course the water often begins by flow- 
ing down some real crack in the rock, which it soon widens 
with its tools ; and thus you may see several gorges roughly 
parallel to one another in different parts of the stream, 
because the cracks or joints in the rock are parallel through 
a large part of the mountain. But in other places gorges 
will be cut, without this assistance, through the hardest and 
most uniform rock-masses, as neatly as if we were to divide 
a bar of soap by drawing a string in one direction steadily 
across it. 

But where do the tools of the stream come from ? How 
do they get into it ? Or have all this sand and all these 
blocks of various sizes been lying about from time imme- 
morial as a coating to the solid earth? We will let the 
grim crags above us answer these questions for themselves. 

Suddenly we step across the last conspicuous ledge of 
rock and have quite a new landscape before our eyes. We 
see the source of our tempestuous little stream — a gloomy 
lake, stretching away towards a semicircle of cliffs, which 
tower almost vertically above it. Seen from this side, the 
water looks indigo or absolutely black ; only when we walk 
round and look out towards the open lowlands do we catch 
some broad and gleaming reflection from the sky. 

These mountain-tarns are among the most beautiful, and 
at the same time loneliest, things in nature. Sometimes, as 
you sit beside them, you will be almost startled by the mere 
sound of a stonechat upon the shore ; in Scotland, or the 
west of Ireland, you may perhaps look up and see an eagle 
sweeping out from the gloom and blackness of the crags. 

On the side of the lake farthest from the semicircle of 
cliffs, there is often a little beach of sand ; even here the 
wind beats the lake up into waves and so manufactures 
pebbles on the shore. The place where the stream runs out 



A MOUNTAIN HOLLOW 35 

is often difficult to trace, since the water escapes among the 
tumbled blocks around the borders of the lake, and only 
collects as a stream lower down, through the union of 
several of its underground tricklings. Similar streamlets 
come down the walls of rock into the lake, and thus there 
is a constant current through it. 

These higher streamlets descend in steep gullies ; but at 
the foot of each there is a great loose mass of angular stones, 
forming a cone stretching up from the lake-shore towards 
the higher crags. Every groove of the rocks has a cone of 
this kind at its base ; it is the simplest form of talus, the 
heap made by the materials that fall down into the hollow 
from above. 

To understand these heaps, we must not be content with 
a clear summer's day when we climb up towards the summit 
of the mountain. We must visit the hollow in rough 
weather, when every groove is filled with a white line of 
foaming water, and when every stone shines with dampness 
and is ready to move easily over its neighbours. Then we 
may hear the clatter of sudden little slips of rock ; we may 
see all round us the work of destruction going on ; and we 
shall learn, indeed, that these cones of debris are continually 
being added to from above. I^he mere force of the rain 
driven by the wind, against which we can scarcely stand 
at these high levels, is sufficient to beat out tiny fragments 
from the crevices of the rocks, to widen these crevices year 
by year, and finally to set a large block rolling down the 
slope. When it once starts, it forms a powerful engine of 
destruction ; it batters at projecting points in its passage, it 
sets perhaps a ton of material moving when it strikes upon 
the steeply piled talus ; and thus it not only breaks up other 
rocks, but it helps the earlier products of decay to move 
lower down the mountain-side. 

Every gusty wind that we know down in the valley is 
intensified at heights of two thousand feet and upwards into 
a destroying storm-blast. The air has few interruptions, 
and moves freely over long distances before it strikes upon 
the mountain-ridges; and there it gets suddenly checked, 
and goes roaring into every hollow, driving before it water, 
and sand, and even little loosened stones. As an example, 
we may note that the winds blow across Ben Nevis from 
November to March at an average rate of twenty-two miles 



36 OPEN-AIR STUDIES 

an hour, and between June and August at eleven miles an 
hour ; but, 44(X) feet lower, in the hollow of Loch Linnhe, 
they blow with rather less than half these velocities. During 
a south and south-west gale on Febraary 21st and 22nd, 
1885, the wind blew at the summit of Beri Nevis from the 
noon of one day to that of the next at about a hundred 
miles per hour, the velocity down below at the sea-level 
being only about thirty miles per hour.^ 

The vigour of the wind in buffeting the peaks of moun- 
tains may be further gathered from the fact that during the 
memorable storm of November i6th to 20th, 1893, the wind 
blew near the sea-level at Holyhead at eighty-five miles an 
hour for four hours together, and reached ninety-six miles 
an hour in the Orkney Isles.^ 

Even on ascending a church-tower, we notice an increase 
in the keenness and swiftness of the wind ; and on the summit 
of the Eiffel Tower in Paris the velocity is three times greater 
than that experienced in the city, only 1000 feet below.^ 

Moreover, the air is far moister, and thus far more rain 
falls, on these higher levels of the hills. It always feels 
colder than in the plains below, although we are in reality, 
by ever so little, nearer to the sun ; and observers in balloons 
tell us how soon they can ascend to a level where the tem- 
perature is below the freezing-point of water. The reason 
for this is that dry air is not heated directly by the rays 
of the sun, but only by actual contact with some hot body. 
Hence the earth or ocean has to be warmed by the sun, and 
the heat is then given up to the air resting upon it. But a 
cubic foot of warm air is lighter than a cubic foot of cold 
air — or, rather, in these great masses of the atmosphere, we 
should speak of millions of cubic feet ; hence a disturbance 
of the balance of the atmosphere occurs where any locality 
becomes heated, the air expanding as it is warmed, and the 
colder denser air pressing in and forcing the warm air 
upwards. As the latter rises, it cools again, especially be- 
cause it has now less of the atmosphere pressing upon it, 
and thus can expand greatly, its heat becoming spread over 
a far greater space than before. Hence the body of air at 

1 ** Meteorology of Ben Nevis," Trans. Roy. Soc. Edinburgh, vol. xxxiv 
(1890), pp. xxxvi, 164, 372, &c. 

' C. Harding, NaiurCf vol. xlix (1894), p. 295. 

' A. Angot, Oomptes rendtu, vol. dz (1889), p. 698. 



A MOUNTAIN HOLLOW 37 

a high level is characteristically colder than that in contact 
with the ground. 

Then, again, evaporation goes on, as we all know, more 
freely in warm air than in cold ; and the air near the earth 
absorbs into itself a large quantity of water in the invisible 
gaseous form. It does not soak it up like a sponge, for the 
particles of water-vapour, in becoming added to those of the 
mixed gases which constitute the air, merely introduce a 
lighter substance into the mixture and increase the bulk of 
the whole. Hence moist air is lighter, bulk for bulk, than 
dry air, and warm moist air is likely to rise most readily to 
the higher regions. 

Air at any given temperature, however, can only absorb 
a certain quantity of water-vapour ; it then has reached its 
saturation-point, and must yield up some of its water-vapour 
in the liquid form again directly it becomes cooled. It is 
scarcely necessary to mention here that this is the cause of 
the sheets of cloud above us on a gloomy day, or of isolated 
clouds at any time. Glouds result from bodies of moist 
air becoming cooled below their saturation-point ; the water 
separates out around the floating dust-particles of the atmos- 
phere in the form of tiny drops, which are so small as to be 
wafted along without falling to the earth. At last, however, 
continued cooling may produce a rain-shower, when the minute 
drops have run together into larger ones, and can no longer 
be buoyed up. 

The level at which clouds can be formed will vary with 
local conditions of climate, and with daily changes of tem- 
perature on the earth itself ; but a level must exist in the 
atmosphere, above every locality, where the temperature is 
below the freezing-point of water, and where any moisture 
separated from the air must take the solid form. At this 
level the delicate cirrus-clouds, or " horse-tails," are formed, 
which consist of masses of snow-crystals supported by the 
air-currents ; in our winter-time, gloomy and denser snow- 
clouds may arise close to the surface of the ground; in 
summer the light cirrus may be four or five miles above our 
heads. The level in the atmosphere above which, even in 
summer, the temperature remains always below the freezing- 
point of water (o^ C. or 32° P.) may be called the snow-level. 
The snow-levels of different localities, when traced from one 
point to another, form a surface which now approaches, now 



38 OPEN-AIR STUDIES 

recedes from, the surface of the ground ; and, if any parts 
of the earth are sufficiently elevated to rise through and 
above this " snow-surface," the line formed on them by the 
local snow-level will be what is called the snow-line. 

Sometimes, when the accumulation in winter is very 
great, snow may lie at levels where the average temperature 
of the year is as high as 3"* C;^ but, in all ordinary cases, 
when we rise above the snow-line, dew cannot be deposited 
nor can rain fall, even in the height of summer. Their 
places are naturally taken by hoar-frost and snow. Evapora- 
tion goes on from the surface of the snow, despite the cold, 
provided that dry air is brought into contact with it ; but 
the chances are in favour of continual deposition of fresh 
material — we have here, indeed, a region of perpetual snow. 

Now, our British and Irish mountains are not so high as 
to reach above the local snow-line ; but again and again we 
can obseiTe how their summits are in the level of the clouds, 
while the valley below is warm and free from mist. As we 
sit by our little lake and look upwards, we notice wisps of 
cloud even now forming among the rocks, particularly on the 
shaded side of the mountain ; soon they are blown away into 
warmer and drier regions of the air, and disappear again in a 
gaseous form. But, as night comes on, clouds will gather all 
along the ridge ; the earth no longer warms the air down in 
the plains and sends hot supplies up to the mountain- tops ; 
the cloud-level drops lower, and the more prominent peaks 
stand out clearly above it. A moonlit jiight is best for 
observing this effect, for then the earth cools rapidly into the 
clear air, and the long banks of cloud lie still and white 
against the hills. 

The ridges are liable to be cloud-capped at any time, 
particularly if the prevalent winds bear moist air with them 
from the sea. This air, already near its saturation-point, 
comes against the hills, and is forced to move towards higher 
levels in order to pass over them. In so doing, it becomes 
chilled below its saturation-point ; the moisture comes out of 
it as a sheet of cloud, one edge of which rests against the 
mountain ; and above this the sky is clear, since the air has 
been thus rendered dry again, though it is even colder than 
at the level of the clouds. As long as the same wind blows, 
bringing in the moist air against the mountain, the clouds 

^ Heim, '* Handbuch der Gletscherkunde," p. i lo. 



A MOUNTAIN HOLLOW 39 

will go on accumulating ; and at last they themselves become 
driven bodily up the slopes and over the crest into the drier 
area beyond. Here, like the little wisps we were watching 
among the crags, they become absorbed again, and the whole 
mass of cloud may thus be continually added to at one end and 
dissolved away again at the other. It will probably not be 
long, however, before further chilling causes the cloud-drops 
to run together, and copious rain to fall upon the windward 
slope. 

Then, on the clear and cloudless nights, dew is freely 
deposited on the mountain. The air is often near its satura- 
tion-point at these high levels, while radiation of heat from 
the rocks and grass is bringing their temperature steadily 
down. Then the film of air in contact with them becomes 
also cooled, and finally yields up its moisture in little dewy 
beads, which accumulate rapidly if the air is in motion, and 
if fresh material is thus brought to the cold surfaces. Often 
the cooling goes on so far that the freezing-point is reached, 
and then the water-particles are extracted from the air in the 
form of delicate ice-crystals, or hoar-frost. 

One of the most beautiful sights upon a mountain is when 
every projecting point of rock and every blade of grass is 
tipped with hoar-frost streamers ; it becomes clear that we 
are not dealing in any way with frozen dew, but that the ice- 
crystals have been deposited as such out of the atmosphere, 
accumulating one on another, the ice -banner sometimes 
pointing in the teeth of the wind, and sometimes curving in 
long plumes in the opposite direction. I have seen the upper 
thousand feet of the Mourne Mountains covered with hoar- 
frost of this kind, so that the accumulation of it during two 
days finally resembled snow. On Ben Nevis, with the ordi- 
nary wind-rate and cold fogs, these crystalline plumes grow 
as rapidly as half-an-inch per hour. 

If all the moisture deposited in one form or another out 
of the atmosphere, at any place during an average year, were 
converted into a sheet of water lying on the level surface of 
the ground, just where it fell, none of it being evaporated 
again or allowed to run away, then the depth of that accumu- 
lation of water, measured in inches, is what is styled the 
mean annual rainfall. Observers at fixed stations collect 
the moisture — dew, rain, hoar-frost, or snow — daily in rain^ 
gaiLges, and carry on their records month by month and year 



40 OPEN-AIR STUDIES 

by year. Thus in time they arrive at a correct average 
statement of the rainfall, which is expressed in inches, the 
hoar-frost and snow being calculated as if melted. Here, 
again, we will take a special instance, showing how the rain- 
fall is greater at high levels, especially where the prevalent 
winds blow from large bodies of water towards the hills. 
On the summit of Ben Nevis, 4406 feet above the sea, the 
annual rainfall is 129.5 inches ; but below, at Fort William, 
29 feet above the sea, it is only 77.3 inches. That is still a 
high rainfall for the British Isles, the eastern counties of 
England having only about 24 inches. 

We are now in a position to realise that the summits of 
our mountains are kept continually damp by dew, which 
soaks into every crevice, and which actually helps to feed the 
streams. Clouds are continually moving over the surface, 
and rain falls far more abundantly than in the plain below. 
The blasts of wind are here felt in all their force ; it is, in 
fact, a region of violence and storm. Besides the mere bat- 
tering of rain and hail, all this moisture exerts a powerful 
chemical action. Rain, while falling, dissolves the gases of 
the air, and in proportions very different from those in which 
they are mingled in the atmosphere. While in 100 cubic 
feet of the latter we have 2 1 cubic feet of oxygen and 79 
of nitrogen, rain-water may absorb 35 parts by volume of 
oxygen to 65 of nitrogen. Iron is common in various com- 
binations in the rocks, and the oxygen, carried downwards 
by the soaking water, tends to make hydrous iron oxides 
along every joint and surface. The brown stains of rust that 
result are the signs of extensive chemical decay. The carbon 
dioxide, also absorbed in larger proportion than that in which 
it exists among the gases of the air, slowly attacks the com- 
pound minerals, making carbonates out of some of their con- 
stituents ; and these carbonates are often soluble, and are 
carried away with the general flow into the streams. Complex 
silicates like felspar become thus broken up, the soda and 
potash disappearing as carbonates in solution, some silica 
being set free, which also passes into solution, and the 
aluminium silicate combining with water and forming a soft 
white powder known as kaolin (p. 21). When one mineral 
of a rock breaks down in this way, and is carried away, either 
in solution or in solid particles, the whole rock soon becomes 
loose and crumbling, and the minerals that could not be 



A MOUNTAIN HOLLOW 4 1 

attacked by natural waters are set free as little grains, to be 
washed or blown down the mountain-side. By insidious 
action such as this, huge masses of rock are eaten into, and 
the storms are always clearing away the detritus and ex- 
posing a new surface to attack. 

Limestones are bodily dissolved by rain-water containing 
carbon dioxide, and we find their surfaces covered with little 
pits and circular hollows. We may often recognise them in 
this way among the other rocks of a hillside ; and in some 
parts of the Alps they are eaten into by the storm-water, 
until the grooves so made resemble gigantic saw-cuta 

For the grandest insight, however, into the assaults of 
weather upon the mountain, we must come up into our 
highland-hollow after a clear cold night. During the day 
all the cracks of the rocks have been filled with water, which 
has become frozen during the hours of darkness. As water 
cools, it contracts in bulk until it reaches 4° C.,^ after which 
it expands again. At 0° C, the freezing-point, it passes into 
the solid state, and a given bulk actually occupies a space 
rather more than an eleventh greater than that which it 
occupied at 4° C. Moreover, the great part of this expansion 
occurs suddenly, at the moment of solidification, and thus the 
water imprisoned in a crevice has no time to ooze out again, 
but exerts a splitting force upon the rock in which it is 
confined. 

It will be well to have this stated exactly. 100 grammes 
of water at 4° C. occupy a space of 100 cubic centimetres; 
at 0° C. this bulk of water has increased to 100.012 cubic 
centimetres ; but at the same temperature it becomes ice 
occupying as much space as 108.992 cc. Another way of 
stating the matter is that 91.75 cubic inches of water at 
0° C. pass abruptly into 100 cubic inches of ice. 

As the sun strikes upon the mountain and heats the 
rocks again, the ice melts, and huge fragments, which have 
thus become wedged out, are dislodged from the cliffs 
above our lake. Frozen water has thus a startling effect 
in breaking up a mountain-mass. Day after day it may 
work in this way, and may shower down stones large and 
small on to the growing talus-cones. The whole mountain 
is, in fact, decaying, and it is being attacked most vehemently 

^ Or a temperature very near to 4° C. ; M. de Coppet gives 3.982° C. 
{NaturCf vol. li (1894), p. 37). 




42 OPEN-AIR STUDIES 

in its higher levels. The stones and gravel that we saw on 
the ascent have all been worn from it by rain and frost and 
slow insidious chemical action. The lower slopes become 
protected by the showers of dSbris ; but the streams wash 
down through these, and use the loose stones as tools to cut 
deep channels in the mountain-flanks. In our hollow itself, 
around the little lake, we can see how the agents of decay 
continually lay bare new surfaces ; and we say that rapid 
denudation is going on. 

Thus, then, we can account for the steepness of the 
crags towards the mountain-crest. The denudation is vio- 
lent, vertical in its character ; and the result is all the pic- 
turesque scenery of peak and notch and gully that makes the 
ridge at sunset look like a black saw against the sky. Our 
semicircular hollow has been cut back on a large scale, 
like the little alcoves over which the waterfalls of the stream 
descend (Plate I). One line of weakness, one principal 
groove where the water rushes down at every storm, has de- 
termined the main recess ; numerous side-streams have done 
their work, and the frost has split off block after block and 
kept the walls almost vertical. For a long time the scour of 
water at the foot was probably suflScient to prevent the Mbris 
from forming banks against the cliff; and the hollow of the 
lake itself may be regarded as resulting from this vehement 
swirling action. It is, in fact, an exaggerated pot-hole, and 
corresponds, in a broad form, to the basins beneath the 
waterfalls in the stream. Another agent, which we shall 
refer to later, has probably helped to keep the. hollow clear 
(p. 56). 

Our mountain-hollow may be called a comber the nearest 
English word for the Welsh cwm, which is applied to similar 
rock-bound excavations. But the most international word is 
cirque, which is used to express the form of the cliff, re- 
minding one of half a Roman circus. When, by continued 
weathering-back, two cirques approach one another on oppo- 
site sides of a mountain-mass, the ridge between grows 
narrower and narrower, until at last it may be a mere knife- 
edge, accessible only to skilful mountaineers. Splendid 
examples of cirques occur on Snowdon, the ridge or arete 
between Cwm-y-Clogwyn and Cwm-y-Llan, where the Bedd- 
gelert path runs up, being only eight feet wide ; while the 
sawlike crest of the Crib-Goch, between Cwm-Dyli and 




WATERFALL forminc. an Alcove in Stratified Rockh, 
Glencar, Co. Sligo. 

ftiB !,) [Pholtgrafhedh Mr. B. Wblc 



"^ 



A MOUNTAIN HOLLOW 43 

Cwm-Glas, is considered good exercise for members of the 
Alpine Club. 

Above us still, in our mountain-hollow, we can see a 
number of pinnacles standing out against the sky. They 
are the masses left behind by the little streams, which have 
cut deep grooves on either side and have in part hollowed 
away the rock behind them. Small as they look from below, 
they tower above us when we clamber up among them ; some 
look as if they must speedily be undermined, and all are no 
doubt decaying. Yet the changes that go on here are slow, 
and the oldest inhabitant of the hillside-farms will say that 
these fantastic rocks have " always " been just as they are now. 

Well, we must admit that in the British Isles denudation 
on the mountains is, after all, a comparatively gentle matter. 
Come to the summit of our ridge, sit on the pile of stones 
which the Ordnance Survey has heaped up as a landmark, 
and look out over the general landscape. Peak after peak 
rises from the highland country near us, but the lower slopes 
are thickly strewn with debris which the streams are unable 
to carry off. The great times of carving and excavation are 
at present over, and we are apt to think that some agent 
more violent than those which we see at work around us first 
made these giant channels between the hills, and then flung 
down the huge boulders into them. 

But the fact is that we have come too late to see our 
mountains in their fullest grandeur. The vast piles of de- 
tritus, the long sweeping taluses, show how much dignity 
they have lost. Many summits in Scotland, like those of Ben 
Nevis or Quinag, are actually buried in loose blocks, so that 
we have to go lower down to see the solid rock exposed. 
Our mountains have been worn down until they have come 
below the level of most vehement attack ; to study denuda- 
tion in all its real rapidity, we must scale another six or 
seven thousand feet, in the Pyrenees, Norway, or the Alps. 

Here matters become more complicated, for we rise 
above the snow-line. On the upper parts of these huge 
mountains all moisture will be deposited as snow and hoar- 
frost. Here and there the bare rocks may get heated by 
the sun, may melt the snow in their crevices, and may be 
broken up by the expansion of the water as it freezes again 
later in the day; but the main mass of snow will go on 
accumulating, slipping off the steeper crags and gathering 




44 OPEN-AIR STUDIES 

thickly in the hollows, forming there broad snowfields, from 
which it is removed in two ways — by the formation of 
avalanches and by glaciers. 

Many crags upon high mountains are so sheer that the 
snow can lie only upon occasional little ledges. Of such a 
character are the great face of the Matterhom, and, still 
more strikingly, the huge conical and spire-like pinnacles, 
the Aiguilles of both flanks of Mont Blanc. In other peaks 
there may be a long steep slope where snow gathers, but 
from which any great accumulation must tend to slip. The 
sides of the huge Alpine valleys similarly offer very little 
resting-ground for snow. A crack forms in the surface of 
the steeply lying snowfield, and any trifling disturbance 
starts the great detached mass down the slope. Carrying 
with it stones and earth and lumps of ice, these last result- 
ing from the compression of the lower layers of the snow- 
field, it plunges headlong into the valley as an avalanche. 

Dr. Pernter ^ of Vienna has given us an account of the 
avalanches in the range of the Hohe Tauem, on the borders 
of Karinthia. It appears that some are caused by the partial 
melting of the snow-sheets by the warm south wind ; gradu- 
ally the water accumulates, and diminishes the friction of the 
ground against the lower surface, which has hitherto upheld 
the mass ; and finally the whole sheet slides disastrously 
downwards. Other avalanches are caused by the slipping of 
newly fallen layers over previously consolidated older ones. 
Their movement is very rapid, and they are preceded by a 
terrific blast of air. One such avalanche witnessed by Dr. 
Pernter filled a valley " for a distance of two kilometres with 
thirteen feet of snow. The avalanche itself could not force 
its way up the side of the opposite mountain, but the wind 
caused by it unroofed a farm-house, 650 feet above the 
valley, and blew in the windows." 

Tlie prevalence of avalanches, as a means by which the 
accumulation of winter snow, and of snow above the snow- 
line, is got rid of, causes certain mountain-pathways to be 
very dangerous in the spring. In many cases the magni- 
ficent roads constructed in the Alps about the close of the 
Napoleonic wars run at higher levels than the old mule- 
tracks, so as to be above the lines along which the avalanches 

^ **A Winter Expedition to the Sonnblick," Natv/re, vol. xlii (1890), 
a73- 



A MOUNTAIN HOLLOW 45 

are likely to break off from the main snow-sheet. This is 
notably the case with the Splugen road, which proceeds at 
first almost horizontally from the pass, and then descends by 
a bold series of curves and tunnels cut in the great cliff 
above Isola. It thus avoids the steep-sided valley which 
Marshal Macdonald traversed with so much difficulty in the 
winter of 1800. Avalanche-galleries, to protect travellers, 
are common at exposed points on any mountain-road. 

The snow may accumulate at high levels to depths of 50 
to 90 metres (160 to 300 feet), and the lower layers in the 
gathering-grounds or snowfields become, as we have hinted, 
greatly compressed and compacted, and, in fact, converted 
into ordinary massive ice. We must remember that this 
results in no way from a further freezing of the snow; 
the term " frozen snow," which is sometimes seen in news- 
papers, has strictly no meaning, since all snow consists of 
ice-particles and cannot be more frozen than it is at the 
time of its formation. But it can have the air squeezed out 
from between the ciystals, as occurs when a good hard snow- 
ball is constructed ; and this is what happens to the older 
snow of a snowfield as the newer layers press steadily 
upon it. 

At first, under these newer layers, we have a snow that is 
firmer, and in which the ice-crystals are compacted together 
into groups, forming little granular lumps, partly trans- 
parent, partly white with air-bubbles. This material is 
known to German-speaking mountaineers as fim, and to 
the French as n^V^. As the surface-snow melts in the sun, 
water trickles in between the granules of the firn, freezes 
there, and surrounds them with a cement of ice ; the mass 
thus caused has been called firn-ice. 

Continued pressure forces nearly all the remaining air 
out of this fim-ice, and a compact layer of ice results. 
The massive ice that is made in this way consists of a number 
of granules from two millimetres to fifteen centimetres ^ 
in diameter, each being composed of one ice-crystal. The 
largest ones occur in the ends of the ice-streams or glaciers, 
and a good average size for these glacier-grains is that of a 
walnut. They fit perfectly into one another, but the surfaces 

* J. C. M'^Connel and D. A. Kidd, " On the Plasticity of Glacier and other 
Ice," Proc. Royal Soc. Lond., vol. xliv (1888), p. 333 ; and A. Heim, ** Hand- 
buch der Gletscherkunde," p. 120. 



46 OPEN-AIR STUDIES 

between them can be seen as the ice slowly melts away in 
lower levels of the mountains. 

This massive ice becomes squeezed out under the snow- 
fields, and oozes slowly down the hollows of the mountains 
in the form of ice-rivers or Olaciers. At the lower end 
each glacier is melted away, at the upper it is continually 
supplied with fresh snow; and thus it keeps in much the 
same position on the hillside. But throughout its length the 
ice is moving forward, as has been shown by the changes in 
the position of stones lying on its surface, and by driving 
stakes into the ice and noticing that they are carried down 
the slope. If a row of such stakes is set up along a line 
across the glacier, it will soon be found that the central 
ones have moved farther than those nearer to the sides. 
The rate of movement is about 4 to 1 6 inches a day, i foot 
per day being a fair average, measurements from the Alps, 
Norway, and the Himalayas agreeing closely. Far more 
rapid movements have been recorded from northern regions, 
but it now seems that even the Muir Glacier of Alaska, an 
unusually swift example, progresses at only 7 feet per day.^ 
The flow is more rapid towards the centre of the stream, 
because the ice there is not retarded by the rocky walls of 
the valley ; the central portion flows, indeed, from three to 
ten times as fast as the margins. Similarly, the upper layers 
of a glacier move more quickly than those that rest against 
the valley-floor. The partial melting that takes place in 
summer also considerably assists the flow, especially in the 
case of a small glacier. Again, where the valley is narrow, 
or where the floor falls steeply, the glacier moves more 
rapidly than in its broader or more gently shelving por- 
tions. 

Some glaciers are mere small patches of ice oozing out 
from the edge of a high snowfield, and falling from time 
to time over the great cliff below in a series of dangerous 
avalanches. Sometimes a glacier of this kind gives rise to 
a new one in the hollow below, where the blocks of ice 
become compressed together again and ooze downwards as 
before. Many glaciers, apparently hanging on the moun- 
tain-side, covered with grey dust blown on to them from 
the rocky walls, are by no means imposing features in the 

1 H. F. Reid, "Studies of the Muir Glacier."* See Oed, Mag., 1892, 
p. 429. 



A MOUNTAIN HOLLOW 47 

landscape, and look mean and dirty after the pure white 
snows above. But a really large glacier is often a magnifi- 
cent spectacle. As it comes round comers of the valley 
in which it descends, it cracks open in a series of deep 
crevasses ; the rich blue ice is seen in their walls, and 
between them the surface of the glacier is rugged, broken, 
and serrated. When a steep place in the valley is reached, 
an ice-fall occurs, the glacier breaking into huge blocks and 
reuniting down below. Here again one can see all the 
beautiful colour of the ice, the pile of angular masses tower- 
ing up the slope like a vast stairway shattered by an earth- 
quake, and gleaming white, or coldest blue, or green, in the 
brilliance of an Alpine sun. On the Furka Pass, to take a 
fine example, we may toil up a long bleak valley from 
Andermatt, and then suddenly come out in view of one of 
the most impressive sights in Switzerland, the ice-fall of 
the glacier of the Rhone. We might wait some time 
before we could notice a change in the positions of these 
freshly broken masses ; but the ice is here descending at a 
comparatively rapid rate, and the glacier is completely torn 
to pieces. 

At its foot, the glacier, where the floor of the valley is 
wide and flat, spreads out like a thick fan, with crevasses 
running from the semicircular margin towards the centre of 
the ice-stream. Often a glacier melts away on the steeper 
slope of the mountain, and ends off in a somewhat narrow 
and irregular tongue. A cave occurs in any case in the 
foot of the ice, where a stream, white with sand and mud, 
runs swiftly out. This stream has arisen under the ice far 
up the slope, partly from the melting of the lower layers 
by the warm earth, partly from the trickling in of water 
from the upper layers as they are melted by the sun, and 
partly from streamlets which have fallen upon the glacier 
in regions below the snow- line, and which have found their 
way to its base down the crevasses. 

The final complete melting of the ice at the foot of 
the glacier adds largely to this stream, and a considerable 
flow of water is the result. The Rhine and the Rhone, 
for instance, both arise thus in the glaciers of central 
Switzerland. 

We have said that the foot of the glacier remains fairly 
stationary. It certainly does not move forward, ploughing 




48 OPEN-AIR STUDIES 

np the land and menacing the peasant with destruction, 
as is often stated in imaginative answers written in 
the excitement of examinations; but in certain times of 
heavy snowfall the lower edge of the glacier advances 
steadily; then in other years it recedes up the slope, as 
the mass becomes melted more quickly than the snow is 
supplied to it above. Observations tend to show that in 
Switzerland the glaciers advance and retreat again in a 
period of from thirty-five to fifty years, and that there has 
been a steady increase in the length of several since 1875.^ 
Of course changes in climate, extending over far longer 
periods, may also be going on, and may ultimately tend 
to increase or to reduce the glaciers in a very striking 
manner. 

Even under existing conditions of climate, and in warm 
countries, glaciers are impressive in their extent. The 
Great Aletsch glacier, in the Bernese Oberland, the largest 
in Switzerland, is fifteen miles (24 km.) long, and in most 
places is a mile acrosa In the Himalayas, moreover, 
where the snow-line lies as high as 16,000 feet, some 
glaciers are thirty-five miles in length. 

The thickness of the ice has been measured by sound- 
ings in the depths of the crevasses, and Professor Heim^ 
concludes that the Alpine glaciers ^re commonly from 200 
to 400 metres thick — let us say, 1000 feet. 

The more we consider these enormous masses of ice, 
the more interesting does their movement seem. The 
precise causes of it have been the subject of many dis- 
quisitions ; briefly, we may say that the granular character 
of glacier-ice seems the most important point to be kept 
in view. All these irregularly bounded crystals, fitting 
closely into one another, are capable, under pressure, of 
rolling over and altering their relative positions. Some 
become, under specially favourable conditions,^ frozen 
together to form a single larger grain ; but the whole 
glacier-mass moves forward, into hollows and round corners, 
as a plastic body. Any piece of ice, moreover, is composed 
of one or more crystals of solidified wat^r ; and each 
separate crystal is capable of altering its form when stress 

^ F. A. Forel, Nature^ vol. xlvi (1892), p. 386. 

2 " Handbuch der Gletscherkunde," p. 79. 

^ See the interesting experiments of Heim, Ibid.^ p. 330. 



A MOUNTAIN HOLLOW 40 

is applied to it.^ Thus, if a bar of ice consisting of one 
crystal is supported at the two ends, while a weight is 
hung by a string from its centre, the ice will bend down 
into a curved form. This plasticity of the individual 
glacier-grain has only recently been brought forward as 
a cause of glacier-motion ; but it is easy to see how it may 
help the whole glacier to fit itself into the irregularities 
of the ground. The phenomenon of the uniting of two 
surfaces of ice when pressed together is discussed, under 
the title regelaiion, in all text-books of Physics, and, with 
notable clearness, in TyndalFs "Forms of Water." Ice 
becomes liquid under pressure; the water formed spreads 
out over the surfaces that are being squeezed together; 
and, the moment that the pressure is relieved, this water 
becomes solid again and cements the two blocks together. 
Thus ice broken by crevasses and on ice-falls will reunite 
into a granular plastic mass, the required relief from 
pressure being aflEorded by the onward movement of the 
whole. 

This movement of the glaciers enables them to play a 
most important part in the denudation of high mountains. 
We have already seen how some glaciers look dull grey 
or brown upon the surface, owing to the immense quantity 
of dust and small stones that are dropped upon them. But 
in addition there is at each side a line of far larger blocks, 
which have fallen upon the glacier from the rocky walls 
of the valley in which it is descending. Frost wedges off 
these blocks in the upper regions, and sometimes torrents 
add material in the lower part of the glacier's course ; but 
the blocks, however huge, are carried downwards by the 
steady flow of the ice, and the valley-walls above the glacier 
cannot become banked up and protected by the products 
of their own decay. The lines of stones thus produced are 
called lateral moraines. All the material carried by the 
glacier is, of course, dropped at the end as it melts away, 
and there forms a great loose deposit known as the terminal 

moraine. 

If we visit the foot of a glacier soon after sunrise, we 
shall see the stones falling over the great ice-slope and 

* J. C. McConnel, "On the Plasticity of an Ice-Crystal," Proe. Royal 
Soc, London^ vol. xlix, p. 325; Emden, "Ueber das Gletscherkoru," Nouv» 
M4m, Soc, Hdv6tique dea Sci, Nat, tome xxxiii (1893), p. i. 



So OPEN-AIR STUDIES 

bounding down into the stream as it flows out below. All 
through the night these stones have been thrust farther 
and farther towards the edffe, and now the sun is iust 
warming them, loosening the grip that the ice has upon 
them, and allowing them to fall in quite an abundant 
shower. At all times of the day some blocks or other are 
about to drop over the edge, but we may not be so lucky 
as to catch them precisely in the act. 

The terminal moraine is undermined and spread out by 
the rush of the stream, and forms a huge bank of boulders, 
pebbles, and sand, stretching away into the open valley. 
Wherever glaciers are at present smaller than they have been 
in the past, we see the old lateral moraines, like the walls of 
some ancient fortification, on either side of us ; the ice-mass 
has shrunk and narrowed, and has left these stone-ridges 
behind it. At the same time the terminal moraine will, as 
the ice retreats, stretch back farther and farther up the slope. 
In the glaciers descending from Mont Blanc, towards both 
Chamonix and Courmayeur, the stranded lateral moraines 
form very conspicuous features. 

Medial moraines also occur ; these are lines of stones 
running down the length of the glacier at a distance from 
the valley-walls. They are easily traceable to the place where 
two glaciers join one another in the higher regions ; here two 
lateral moraines meet, and are carried on together as a single 
medial moraine. Wherever the glacier, moreover, breaks 
against a prominence of rock, and flows round it on either 
side, uniting again below, a medial moraine is likely to be 
formed ; so that sometimes seven or eight lines of debris 
may be seen running down the length of a great glacier. 
The work done by ice in this way as a carrier is greater than 
that of any other agent ; blocks as large as houses can be 
conveyed many miles from their parent source and deposited 
as mysterious strangers in the great terminal moraine. 

In some countries the snow-line is so low, or the accumu- 
lation of snow in some mountain-hollows is so great, that 
glaciers are able to descend to the level of the sea. Then 
there is, properly speaking, no terminal moraine ; the end of 
the glacier, continually pushed forward into the sea, becomes 
floated up, since ice is lighter than water; the crevasses 
become filled with the moving water, and huge masses of ice 
are broken off as icebergs. They go floating away upon the 



A MOUNTAIN HOLLOW 5 I 

ocean-currents, carrying theii* load of debris from the land, 
until they are at last melted in warmer waters. If there is 
a regular drift of icebergs in a particular direction, towards 
a latitude where they all become melted away, a sort of 
scattered terminal moraine occurs there, forming a vast bank 
beneath the sea. A deposit of this kind is being produced 
in the Atlantic Ocean, where the land-ice borne on the 
Labrador current meets the warmer waters from the south. 
Floating ice, then, carries coarse materials to far more 
remarkable distances than any ordinary glacier. Whether 
borne by a glacier or by floating ice, boulders deposited in 
a distant area are styled, from their wandering character, 

erratics. 

There is no wonder that the streams rusTiing out through 
the terminal moraines of glaciers are white with mud and 
sand. But, if we enter the ice-cave, we shall see that the 
stream is already muddy when it issues from the glacier; 
the material carried along by it must have been gathered 
farther up the slope. As a matter of fact, the crevasses of 
glaciers allow of numerous stones falling to the bottom of 
the ice ; there they become held in it, and serve as formid- 
able tools for cutting into the rocks below. The fine dust 
and sand, in part falling from above, in part produced by 
this cutting action, works like sand-paper in smoothing the 
floor over which the glacier moves. These materials, accumu- 
lated beneath the glacier, have been styled the ground- 
moraine. Wherever glaciers have shrunk, or have sunk 
farther into the valley that is continually being deepened 
under them, we see the smoothed rocks left behind to bear 
witness to this scouring action. Some rocks, such as lime- 
stones, take a polish from the passage of glaciers over them ; 
others, such as granites, are only ground down to a broad 
clean curving surface ; sharp scratches occur in these sur- 
faces, and sometimes also coarser grooves, where the larger 
stones have cut into the more uniform work of the fine sand. 
Eocks that have been treated in this way are said to have 
suffered from glaciation, or to have been glaciated. 

The tendency of such grinding action is to smooth off 
and round every angle of an obstacle beneath the glacier, 
such as a projecting mass of rock in the valley-floor ; but the 
front of any rock which faces down the valley will be left 
fairly rugged, though the glacier grinds away the back into 



52 OPEN-AIR STUDIES 

something like a dome. A series of such rocks, when revealed 
to us by the retreat of the glacier, will give a hummocky 
appearance to the valley ; on going up towards the glacier, 
we see merely the rugged ends of these bosses ; on looking 
down the valley, all their smoothed and rounded surfaces are 
exposed to us. It is said that the resemblance of a group of 
such glaciated rocks to a flock of sheep lying down gave rise 
to the name roches moutoim^es, by which they are now 
known over all the world. MoutonrU^ however, means pro- 
perly " frizzled like a sheep's back," and was a term applied 
to wigs ; and the hummocky surface of a glacier-floor cer- 
tainly reminds one more aptly of an old-fashioned wig. 

When we see whole mountain-walls smoothed over in this 
way, and the floor of a valley for miles carved into roches 
moutonn4es, we are apt to get an exaggerated notion of the 
powers of glaciers as agents of excavation. As a matter 
of fact, the valley is constantly being deepened by the 
swirling action of the streams beneath a glacier, and every 
new surface exposed is promptly scoured smooth by the 
stones held in the ice. But it appears that the ice itself is 
so plastic that the upper layers of a glacier will move over 
the lower ones, if the latter encounter a serious obstacle ; and 
hence the glacier itself is probably not a more gigantic agent 
than an ordinaiy mountain-torrent in cutting out a valley- 
groove. But the special feature of glacier-action is that the 
ice removes on its back so much debris which otherwise 
would cumber the mountain-side ; it keeps the upper preci- 
pices always clear, always exposed to the renewed attacks of 
frost. Glaciers thus largely assist that vertical form of de- 
nuding action which we have seen to be so characteristic of 
the higher regions of the mountain. 

Huge pot-holes may in places be excavated beneath gla- 
ciers, by the cascades of water derived from the melting of 
the upper surface of the ice. These waterfalls go thundering 
down into the crevasses, and are kept sometimes steadily at 
work, the crevasse continuing to open at the same point of the 
valley, despite the onward flow of the glacier. They gradually 
cut shafts for themselves, down which they pour, and which 
are known as moulins, or glacier-mills. The rush of water thus 
beats upon any loose stones below and carves out holes and 
basins. The shifting of the moulin, which often occurs, as it 
cuts its way back in the ice, may in time produce consider- 



A MOUNTAIN HOLLOW 53 

able basin-like depressions in the glacier-floor, the surface of 
these hollows becoming striated and polished by the action 
of the ice which enters them.^ 

When the ice diminishes, the work of these mills is re- 
vealed to us, as in the Gletschergarten of Lucerne (p. 32). 
Moreover, the larger rocks borne by the glacier are often 
left stranded in strange positions on the mountain-sides. 
The finer material of the moraines may eventually be washed 
away, and these perched blocks remain conspicuously over- 
looking the present valley. Perched blocks are often thus 
seen resting on the backs of roches moutonndes. 

Finally, the terminal moraine must in part consist, though 
in a comparatively small degree, of the stones that have come 
out from beneath the glacier. These will have been them- 
selves strongly scratched and striated, often in several direc- 
tions, as they are turned round and round under the ice. 
Where the glacier descends to the sea-level, they may remain 
stuck into the base of the icebergs, and become floated away 
into regions far removed from glaciation. 

So much for our excursion into the higher regions of 
the earth. We may now be convinced of the truth of our 
observation on our own mountains, viz., that denudation is 
far more rapid, more serious, more precipitous in its effects, 
near the summits than on the valley-sides. The pinnacles 
that loom above us as we look up from the shore of our 
little tarn are models, as it were, of the aiguilles of Mont 
Blanc, or even of great mountain-peaks like the Grivola or 
the Matterhom. When, after a sudden shower, we hear the 
stones rolling down the gullies and scattering upon the fan- 
like talus, we can form some notion of the constant crash of 
ice-loosened blocks into the glacier- valleys of the Alps. No 
lecture in geology was ever so impressive to me as a few 
words of Mr. W. F. Donkin, describing how he and his com- 
panions camped one night in a hollow under the ridges of 
Mont Blanc, and watched a huge rock leaping down towards 
them, tracing its course by the showers of sparks that it 
drove out of the granite wall. The fallen blocks upon our 
own slopes point to action almost as violent ; witness the 
superb masses in the Pass of Llanberis, which, though their 
fall is now luckily rare, are fully Alpine in their grandeur. 

1 See T. D. La Touche, "The Erosion of Rock-Basins," NaturCi vol. 
xlix (1893), p. 40. 



54 OPEN-AIR STUDIES 

But is there no other resemblance between our mountain- 
hollow and the Alps ? Look carefully at the outlines of the 
rocks that lie between the wall of crags and the steep descent 
into the valley. The floor of the hollow itself, unless the 
taluses have crept too far across it, and the numerous swell- 
ing bosses of rock within it, are wonderfully smoothed. The 
outer rim of the lakelet shows the same rounding and smooth- 
ing ; and here and there, on the descending slope, we look 
down on the bare back of a dome-like rock, only partially 
invaded by the damp green moss. Surely there is a mean- 
ing in these carving outlines. (See frontispiece.) 

The dome-like rock faces down the slope as a steep little 
crag, in contrast to the smoothness that it shows upon the 
side towards us. Surely we have here the features of an old 
glacier-floor, with veritable roches moutonn4es. 

If so, we may well look further. There are suspicious 
groovings on the rocks nearest to us ; but these may have 
been caused by the constant run of small stones over them 
during storms. But turn back the thin covering of grass 
and moss from one of the more protected surfaces; here 
we find cats and scratches, mostly running in one direc- 
tion, beautifully preserved, and unmistakable as signs of 
glaciation. 

It will be worth while now to go down to the stream 
again, where it has carved a section in the gravel of the 
slope, and to see if any of the loose stones have scratches 
on them, as if they had come out from beneath a glacier. 
We may have to search for a long time, since much of this 
broad talas is of fairly modern origin ; but in spots where 
the materials are slate or limestone, or any rock likely to 
receive scratches easily and yet not to be broken up into 
powder, we may be rewarded by a rich find of Striated 
stones. Sometimes, under a mere superficial coating of 
fallen blocks, we may come upon a trae terminal moraine, 
with great masses dropped from the surface of the glacier 
and scratched stones thrast out from below. These marked 
stones will often be the first things to reveal to us the former 
presence of glaciers in the district which we are examining. 
Such stones may have been floated hither in the base of ice- 
bergs when the present land lay beneath the sea ; but, when 
we find them in conjunction with striated surfaces of solid 
rock, and with roches moutonn4es pointing in a fairly uniform 



A MOUNTAIN HOLLOW 55 

direction, we may be sure that we are actually standing in 
the track of an ancient glacier. 

It is' only in the last fifty or sixty years that the meaning 
of such striated surfaces has been known to us. Even in 
Switzerland, when De Saussure wrote his famous " Voyages 
dans les Alpes," they were not connected in the minds of 
observers with the former extension of the glaciers. But 
now, thanks to Agassiz, Forbes, Ramsay, and other writers, 
we have been taught that vast areas of our British Isles were 
at one time covered with moving ice. How much of our 
glacial deposits were laid down on dry land, or how much in 
seas in which floating ice abounded, is still a matter for dis- 
cussion ; but again and again the smoothed rocks and roches 
mouton7i4es show that genuine glaciers were at work. 

Indeed, most of our mountain-hollows have been glaciated. 
The Snowdon district provides us with admirable examples, 
conspicuous among them being the lonely hollow of Cwm-glas 
(see frontispiece), into which we can ascend from the centre 
of the Pass of Llanberis. There is a light bridge leading to 
a farm across the stream, and then we go up to a huge round- 
backed rock, the steep end of which faces down towards us. 
This is the great roche moutonn^e of the lower portion of the 
cwm. The loose blocks around, and in the soil beneath us, 
are part of the local moraine, and are mingled with those left 
by the greater glacier that once swept down the pass. In 
those days the craggy walls were doubtless far higher, as may 
be judged from the enormous debris on the slopes ; and above 
them were hollows full of ndv^ leading up to the snow-peaks 
of the central mass. We may now pass round the great 
roche moutonn4e, noticing the perched blocks upon other 
similar mammillated masses which project out below us 
towards the road. Somewhere in the left-hand curve of the 
cliff that now faces us, we shall find a steep passage leading 
into the upper cwm ; and by this we can ascend to two desolate 
little lakes. In the height of the tourist-season, when hun- 
dreds of visitors stand daily on the crest of Snowdon, Cwm- 
glas remains one of the noblest and loneliest spots in Wales. 
The road is lost sight of some 1 500 feet below ; the precipitous 
semicircle of crags, ranging round us from Crib-Goch, forms 
a gloomy and often cloud-capped background ; and the grey 
floor of the cwm, with its two sunless little lakes, lies strangely 
bare beneath us, completely smoothed by glacial action. 



56 OPEN-AIR STUDIES 

But similar hollows abound in the uplands of North Wales ; 
the corries of the Scotch highlands, as we may note again 
and again, have been moulded and finished off by glacier-ice ; 
and the pale quartz-hills of Connemara, the granite chain of 
Leinster, and the Reeks of Kerry, all give evidence, by their 
striated surfaces, of recent glaciers in our islands. Near 
Pinchley, in the north of London, scratched lumps of hard 
chalk and other stones, with rubbed fossils carried from a 
distance, are found freely in the brickyard-clays. Near 
Dublin, the hollows of the granite mountains, and all the 
surface-gravels of the county, are full of limestone pebbles, 
exquisitely scratched by glacial action. Upper Lough Bray, 
a favourite resort in the Wicklow highlands, is closed on the 
higher side by the characteristic cirque of precipitous rock, 
and is banked up on the lower side by a coarse terminal 
moraine. The schistose hills, again, beyond Lough Tay, 
farther to the east, are strewn with huge erratics of granite 
carried from the central range. The assistance given by ice 
to the formation of cirques may be realised in the higher 
Alps of Switzerland. Here frost-action and the battering of 
mountain-winds are the active agents in cutting back the 
walls of rock, and vertical cliffs of semicircular form result, 
whenever one part gives way more readily than another. 
But the snow that falls so freely slips down these precipices 
and gathers at their foot ; any snow that manages for a few 
days to cling to the wall finally slides into the hollow, carrying 
loosened stones with it and helping to cut grooves in the 
rock-face. At the base of the cirque, in what seems an 
absurdly limited space, a glacier is formed, which flows out 
at the open side in a steep ice-fall. The blocks torn off by 
denudation become swallowed up in the snow on the surface 
of the glacier, and only a few enter the hollow itself down the 
crevasses ; the ice thus protects the hollow, keeps it clear, and 
smooths and striates its floor. In one of the superb photo- 
graphs taken by the late Mr. W. F. Donkin (Plate II), we 
see such a cirque at the base of the peak of the Matterhorn ; 
and it is, as it were, a vivid restoration of the former condi- 
tion of our British mountain-hollows. Were the little glacier 
to melt away, a tarn would be left, with a striated floor, 
beneath the grim theatre of the cliffs, like those of Cwm-glas, 
or Moelwyn, or Llyn-y-Gader on Cader Idris. 

Two of the barest and clearest regions for the study 




»™ n.l SNOW-FILLED CIRQUE 

AT THE Base of the Mattbrhorn, Switzerland. 

t Phtlrgrnflt if Iht Ult Vb. W. F. Dohkin, ;//(r«i(iui(^U«nt.%i«i»w.%.(>i. 



A MOUNTAIN HOLLOW 57 

of perched blocks and roches moiUonnSes are the dark hollows 
of Loch Coruisk in Skye, and the more accessible region 
south of Killamey, along the road from Kenmare to Glen- 
garifiE. Let ns travel thither, and to Switzerland also, to 
continue our studies when we can. Meanwhile, any simple 
mountain-hollow will have tauerht us much in an afternoon. 

And now, as we descend in the twilight, the clouds are 
already gathering on the crests behind us. We come down 
among the great loose blocks again, critically inquiring 
which of them have merely fallen from above and which 
have been stranded by ice-action. Some, like the grey 
flinty boulders so common on the hills around Llangollen, 
are obviously strangers, and must have been ice-borne from 
a considerable distance. When we at last strike the high- 
way and tramp homeward through the dark, we can still 
hear the far sound of waters falling across the blackness of 
the rocks. And we know now that work is going on up 
yonder, and that next morning the sun will send his rays 
into the hollow, already shining upon new things and spying 
out the changes of the world. 



CHAPTEE III 

DOWN THE VALLEY 

The course of any river is full of variety, as we follow it 
down from its source in the hills, through the long windings 
of the valley, across the open plains, and away to the distant 
sea. On every side there are things to interest us, and 
the river itself is the moving spirit of it all. Oar great 
cities would not be where they are were it not for tlie 
rivers, which gave water to the early inhabitants before 
the days of deep wells and costly aqueducts. In many 
cases the town was established where ships, the light sailing- 
vessels of former days, could come up and land their 
merchandise direct upon the quays — ^just as great steamers 
still do below London Bridge, or at the Broomielaw in 
Glasgow, or along the Custom House quay in Dublin. In 
other cases the river divided hostile tribes, and the town 
grew up at some ford, where it was necessary to plant a 
fortress and to keep a constant watch. Whether we travel 
down the Thames, the Loire, the Danube, or the Rhine, 
we see how the flow of the water and the form of the river- 
channel have had their influence upon history. And then, 
besides all this, long before man came into the country, the 
river was working out an elaborate history of its own. 

Many streams have simple beginnings, just as we saw 
among the barren highland rocks. The rain falls, and 
leaps in tiny cataracts down every crack and groove ; on 
some shelf the water is stopped, and gathers as a little 
lake, or forms with the mosses a soft mountain-bog ; from 
this a true streamlet rises, finding its way down among the 
grass-slopes and the fallen stones. 

In some places, however, this water sinks in and dis- 
appears. Rain falls on sandstone or common limestone, 
where it becomes soaked up, and may sink to considerable 
depths. Such rocks, through which water can flow, are 

called permeable rocks ; the water finds its way between the 

58 



DOWN THE VALLEY 



59 



mineral particles, or even, in the case of limestone, dissolves 
the material and works out little channels for itself. In 
our summer, the air is so warm and the days are so long 
that the rain which occasionally falls and sinks in becomes 
dried out again in the form of invisible vapour, and thus 
does not help to form an underground supply. But the 
winter rainfall, on the other hand, produces a quantity of 
water which flows slowly through the permeable rocks, and 
this is the supply that is often reached by the wells in old 
villages and farms. The ground becomes, in fact, water- 
logged, because the water cannot sink indefinitely towards 
the centre of the earth. It is soon stopped by some tm- 
permeahle layer of rock, such as clay or granite, and con- 
tinues to gather in the mass above. If the layers of rock 
have a slope in any particular direction, the water will flow 




L 
C 



Fig. 2.— Section illusteatinq the Origin op Springs. 
A, inland heights ; L, limestone ; c, clay. Springs will emerge at B. 



down this as long as there is some means of escape at the 
other end. 

Imagine (fig. 2) a great layer of limestone resting on a 
layer of clay, and both tilted up so that the higher end forms 
the crest of a range of hills; and let the lower end come 
down to the sea-side, forming a limestone cliff, with the clay 
just showing on the shore beneath. Eain will fall heavily 
upon the heights, and will, in the colder months, accumulate 
as a great body of water in the limestone. The tilt of the 
rocks will cause this water to flow towards the sea, and it will 
produce a number of little streams gushing out over the clay 
surface on the shore. Here we have a line of springs formed, 
which will flow steadily so long as a good rainfall — especially 
a good mnter rainfall — is kept up on the higher ground 
inland. 

Springs arise where underground waters find a con- 



6o OPEN-AIR STUDIES 

venient outlet. When the gathering-ground of the water 
is high, we may sink a well upon some much lower 
portion of the permeable rock, and thus form an artificial 
spring. A " head " of water occurs in the distant mass at a 
higher level, which presses the water upwards in the outlet 
provided by the well, and forces it to flow out upon the 
surface. 

Sometimes we may find a permeable rock lying between 
two impermeable masses, and the whole three layers may be 
bent into a basin-shaped form (fig. 3). Thus on all sides the 
permeable rock is exposed at the surface by this upward 
bending, and receives rain, which sinks into it. But the 
water runs down and accumulates in the centre between the 
two impermeable layers, thoroughly waterlogging the mass. 




% 



FiQ. 3.— Section showing Principle op Artesian Springs and Wells, 

AND Origin of Bournes. 

B, pervious stratum ; a and c, impervious strata ; 8, sea-level. Bournes 
may arise at x and x', and an Artesian well may be made at w. 



If we now bore down through the upper impermeable layer, 
anywhere near the centre of the basin, the water will rise 
freely ; and, if the sides of the basin have been bent up high 
enough, it will flow out copiously as a fountain on the sur- 
face. Wells made under these conditions are called Artesian 
wells, from the fact that successful ones were constructed in 
the French province of Artois as early as 1 126 A.D. 

It will be clear that any permeable layer of rock will be 
drier near its upper surface, and that the water stored up in 
it will rise to a certain level in the mass, this level being 
nearer the surface at some times than at others. Any natural 
excavation or hollow which reaches down to the lowest of 
these variable levels will be occupied by a permanent spring. 
Many other hollows will be full of water in certain seasons 
only — usually after a succession of wet winters — and may 



DOWN THE VALLEY 6 1 

perhaps remain dry for several years together. Such tem- 
porary springs are called Bournes in the south of England, 
and are common on the surface of the soft white permeable 
limestone known as Chalk (fig. 3). 

Water that has thus passed through a considerable mass 
of rock becomes filtered, and issues in most cases as a de- 
liciously clear and cool spring. Near Albury, under the 
Surrey Downs, there is the famous Silent Pool, where the 
water comes out of the chalk along the surface of more 
clayey rocks, and is so transparent that one may stoop down 
and see the fishes apparently swimming in pure air. It is 
difficult to tell where the water below us actually begins. 
But this water has dissolved calcium carbonate (carbonate 
of lime) in its passage through the limestone, and is by no 
means chemically pure. Any material, however, that may 
have been held by the water in suspension, when it flowed 
on the surface of the Downs, has been completely filtered 
out during its underground wanderings. 

Other underground waters gather compounds of iron in 
solution, and these compounds break up and oxidise on 
exposure to the oxygen of the air, forming hydrated iron 
oxide, which stains the water brown ; this substance is itself 
insoluble, and is deposited as a film on twigs and stones over 
which the streamlet flows. In the neighbourhood of copper- 
mines, again, the rocks are sometimes wonderfully stained 
in vivid greens and blues, by the deposition of compounds 
of copper from a soluble condition in the springs. 

Sometimes in a steep country-road, such as the lanes 
leading up over the sandstone of Leith Hill in Surrey, 
we may see, after rain, tiny examples of springs and 
streamlets, rising and bubbling through crevices in the 
surface. The ground below us has become temporarily 
waterlogged, and the little tricklings that come out along 
the cracks and easiest passages soon cut out channels for 
themselves in the roadway, just as streams do in a moun- 
tain-side. 

Thus some rivers may arise in a series of well-marked 
springs, others from the outlets of mountain-lakes, and 
others direct from the melting foot of a great glacier. But 
the majority have their sources in a vast number of little 
tricklings, which wander through some soft bog-land on the 
upper levels of the hills. In our visit to the mountain- 



62 OPEN-AIR STUDIES 

hollow, we have already noticed such waters running through 
tiny channels just below the surface of the ground. They 
unite into little but well-defined rills, hundreds of which 
may go to form what we call a stream. And then some- 
how, with scarcely a distinct beginning, this stream leaps 
and murmurs on the hillside as a thing that can no longer 
be overlooked. Afar off we can see its waterfalls foaming ; 
its course can easily be traced across the brown and purple 
of the moorland ; and on either side of it the heather will 
shrink away, and grass and bog-moss will form soft green 
borders to the waterway. The old settlers planted huts 
beside it, and drove their cattle across the fords ; it became 
a feature of the highlands, something distinct and interest- 
ing, a river at last worthy of a name. 

Now, if we are going to study a river-valley, we may 
as well choose one that has plenty of variety, and that will 
show us the river in many moods. Let us come away into 
the eastern Alps, into the mountains of Tyrol and Karinthia, 
where the rocks and waters are always fighting it out one 
against the other. It is not at all a bad thing to look 
occasionally at the great showy diagrams of the world, and 
then to come back to our own islands with the certainty 
that Nature is at work there also, though the illustrations 
are on a smaller scale. 

It is a wonderful landscape that greets us as we rise in the 
early morning, after our long railway-journey across the heart 
of Europe. Our Tyrolese village, with its square white houses, 
roofed with pine-chips, and its church-towers terminating in 
quaint vermilion bulbs, lies still and dark between the forests 
of the valley-head. A band of cloud still wanders slowly 
between us and the upper pastures, where two or three brown 
chalets are catching the first shafts of sunrise. Along the 
high-road, the road to Karinthia and the east, a white- sleeved 
and blue-aproned peasant is driving some fifty or sixty goats 
with tinkling bells. The clock on the old market-house 
strikes four, and we look up and see that the clouds have 
already almost left the woodland. All round us the peaks are 
rising in a pale blue air of morning — not the great snow- 
masses and glacier-basins of Switzerland, but mountains 
stranger and more fascinating than these, crest and ridge and 
pinnacle of clear grey limestone ; and to-day each ledge is 
marked by freshly fallen snow, which picks out the outlines 



DOWN THE VALLEY 63 

of the crags, and which nowhere veils them. The level sun- 
light makes all the easteni side of these pinnacles a warm and 
golden brown ; we can see the deep clefts and knife-cuts, as 
it were, between them, and the steep shoots of fallen stones 
in every groove beneath the crags. If a block falls now, we 
may hear it in the stillness, leaping in great bounds down the 
grey talus, and starting a rattle of smaller ones along its track. 
Those peaks and barren walls not only mark a region too high 
and cold for trees ; they also extend wherever denudation is 
still active, the limestone, with its huge vertical joints, send- 
ing down block after block, and oflfering no resting-place for 
the fir-woods. Wherever the layers of the rock are bent into 
long sloping curves, with no sheer crag above them, there the 
trees have climbed up in safety, and look down the precipices 
upon the denser woods below. 

Wherever a recent fall of rock has occurred, the scar upon 
the mountain is pale yellow or orange-brown, the colour 
gradually darkening as weathering goes on, until the surface 
again becomes uniform and grey. We have only to glance 
round to see how frequent such falls are, and how the taluses, 
concerning which we speculated among our British mountains, 
are here growing almost before our eyes. It is fairly easy 
to distinguish the recently fallen from the older blocks upon 
them ; and away there in one place an unusual down-rush 
has crashed into the lower forest, rooting up the spruce- 
firs and the larch-trees ; and their dead stems, sloped over 
towards the valley, are seen in forlorn clumps here and there, 
surrounded by angular blocks of limestone. The grass has 
gone, the whole loose slope of the forest has been channeled 
out, and the track of the great stone-slide resembles the 
hollow of a stream. 

Among these broken forest-slopes, between the clumps of 
rhododendron, and whortleberry, and vigorous heather spread- 
ing towards the open air, we find damp little patches of bog- 
moss and rich grasses, where springs, fed by dew and snow, 
gather and begin to bubble forth. All these go to feed the 
rapid torrent down below, which is bridged by the high-road 
in the village. 

If we were to come just as the winter snows are melting, 
each of the humble tributaries of this torrent would itself be 
seen in all its glory. At present they are lost among their 
great stone-banks, among the conical taluses in which each 



I 



% 



64 OPEN-AIR STUDIES 

one ends towards the valley. But the stones in these cones 
are often rounded ; the water has evidently strength enough 
at times to roll one against the other ; and the wonder is that 
the central valley is not choked up by the activity of these 
irregular side-streams. 

On the eastern side of the Arlberg Pass, leading down to 
Innsbruck, one may see magnificent cones of this kind, at the 
base of the most insignificant grooves in the upper rocks. 
Year after year the streamlets rise in flood, and shoot out 
the debris which is daily collecting in the cleft. The huge 
cone, on which vegetation tries here and there to cling, 
receives a new coating, and sheds some blocks, new or old, 
into the valley. Like a cloud-banner gathering on a moun- 
tain, it is constantly being added to at one end, and carried 
away piecemeal at the other. Frost, and the insidious root- 
lets of plants, and mechanical grinding together in the waters, 
finally break up the lower blocks ; and the main stream has 
power at these high levels to carry off the detritus, and to 
allow of further accumulation at the upper end. 

This " creep " of the whole hillside downwards, leaving 
the crags as much exposed as ever to the attacks of denuda- 
tion, is a feature of any steeply sloping country. Our old 
buildings frequently give evidence of it ; thus the Abbey of 
Valle Crucis, near Llangollen, built in 1200 A.D., is buried 
on its north side some seven feet by the creep and accumula- 
tion of the fields, which now stretch evenly from it towards 
the valley-side, with walls and houses built upon them. The 
cathedral at Lismore, again, on a steep slope above the Black- 
water, is similarly banked about with earth, which seems to 
have crept down upon it from the south and to have flowed 
gradually round it. Of course such evidence of forward 
movement of the soil can be best gathered where the 
building which has formed the obstacle has been allowed a 
long period of disuse and disregard. 

It is obvious that the river in our Tyrol village must still 
be powerful enough to cut out its course and to deepen the 
whole valley in which it runs. Eecords of floods and of dis- 
astrous denuding action are abundant in the history of the 
village. Houses have been cut in two, road-embankments 
have been swept away, whole fields have been swallowed up 
in stones or carried down into some neighbouring hollow ; 
and this sort of thing may happen every six or seven years. 



DOWN THE VALLEY 6$ 

giving the inhabitants a continual struggle with the stream. 
In places the pebbly area on either side has been abandoned 
to a rough growth of young willows, through which a few 
shifting paths lead to the swift green river, the actual bank 
of which is always varying its position. Where such varia- 
tions become dangerous, embankments are built out, in stone 
and timber, and attempts are made to " correct " the river 
and to give it a fair straight course. All the bridges are 
made of wood, and can be repaired by local carpenters ; a 
stone bridge would be so much waste of time and money. 
Even the side-streams, which may be dried up for half the 
year, have their floors artificially paved, and are conducted 
with care in stone-lined channels across the slopes. Every- 
where the water, armed with the stones supplied to it from 
the crags, is recognised as an enemy, as a battering, cutting, 
and swirling agent of destruction. 

To pass down one of these valleys of the Eastern Alps 
after a season of storm and flood is indeed a lesson in denuda- 
tion. Among the undermined and shattered houses, every 
active peasant is turned out to cope with the pebbly wastes, 
which have encroached upon the highways and the fields. 
The women, with baskets on their backs, are working knee- 
deep in the stream, bringing loads of stone for new embank- 
ments, until the water is "corrected" once again. Here 
and there, in the narrower gorges, we may find the road 
carried away for several yards, and timbers laid down provi- 
sionally across the gap, until a new foundation can be built 
up firmly from below. 

The great ravine of the Valle del Ferro in the Venetian 
Alps, through which a railway now connects Karinthia and 
Italy, shows striking examples of the excavating action of a 
torrent. Here working in behind some projecting spur, and 
widening a vertical joint until the little promontory becomes 
an islet ; here battering at the heavy masonry that supports 
the road, until foreboding cracks open in it upwards from the 
base ; here taking advantage of some fold or grouping of the 
layers of the limestone rock, and eating out caves at the foot 
of the enormous precipices — everywhere the river can be seen 
in its full health and strength, fashioning its own gorge, 
rolling down the pebbles along its bed, and cutting like a saw 
across the very ridges of the Alps. 

As we leave our village in the valley-head, we soon come 

E 



% 



66 OPEN-AIR STUDIES 

to a region where no fnrther cnltivation is possible, and 
where the ch&lets have been posted on green ledges high up 
above the stream, or have altogether vanished, owing to the 
steepness of the mountain-sides. We enter, in fact, one of 
the gorges or cafions ^ that are so typical of the excavating 
region of a stream. 

The torrent, if left to itself, would naturally cut a deep 
vertical cleft in the rocks presented to it. But to do so it 
must work rapidly ; for other agents are all the time smooth- 
ing back the walls of the groove, sending down taluses into 
the direct course of the water, and tenfing to produce an 
ordinary valley with gently sloping sides. Some of these 
cafions, as the Americans call them, are so surprisingly sheer- 
sided that older observers used to consider them as great 
rents in the earth into which the rivers had found their way. 
Everything goes to show, however, that they are merely 
repetitions on a large scale of the little gullies that occur in 
any mountain-streamlet. The water has laid hold of some 
line of weakness in the rocks, and has worn out its channel 
energetically along it. All rock -masses are traversed by 
thin cracks, frequently running parallel to one another over 
great distances, and known as joints. In some cases these 
joints are due to the shrinking of the rock after it has been 
formed, as occurs in many melted rocks on cooling ; in most 
cases some internal movement in the earth has twisted the 
rocks, and has produced a great series of parallel and inter- 
secting cracks throughout them. These joints, as we must 
have noticed again and again, enable the rocks to be broken 
down by frost or by quarry men in huge masses at a time ; 
they also serve as ready assistants to the river. One set of 
them is likely to be practically vertical, and the water may 
happen to run approximately in this direction. Some one 
joint is laid hold of, and is rapidly widened by the flow. 
Its walls, owing to the parallel joints in the mass, become 
worn back vertically, the rock flaking off in slabs on either 
side ; and the gorge, when once started, may weather back 
and widen at the top, but will deepen and deepen, until the 
torrent flows in a mere knife-cut of a valley at the bottom, 
its sides towering almost sheer in cliff and terrace to a height 
of half-a-mile or more. In the famous ravine of the Via 
Mala, on the Spliigen Pass in Switzerland, the lowest cut is 

* Prmiounoed "oan-yona," 



DOWN THE VALLEY 67 

in places oblique, and is so narrow that, on looking into it, 
the overhanging side conceals the stream from view. In 
all cafions it is interesting to see whether the directions of 
jointing, or the relations of hard and soft rocks lying against 
one another, have influenced the general direction of the 
water-flow, and consequently of the resulting gorge. 

In the ravine we now enter, nothing strikes us so much 
as the ease with which it might be choked for a time by 
any ordinary rock-fall from its sides. Such falls must 
speedily be obliterated by the torrent, or the period of 
excavation would soon be over. As we go down the road, 
which is in one place cut in the wall of the precipice, in 
another built out into the stream, we see above us steep 
side-gullies opening into cirques among the higher peaks. 
Stones stand in the mouths of some of these, ready to be 
driven over in some day of desperate storm. A few such 
blocks might serve to close the channel altogether. But 
the force of the river is so great that it bursts such dams 
again unfailingly ; a few masses are left, like islets towering 
from the foam, and the others, shattered and broken down, 
are added to the pebbles which rattle against and under- 
mine the cliflfs. The river again asserts itself and continues 
to deepen the ravine. 

Such a gorge, with occasional glimpses into the recesses 
of the mountains far above, may continue for seven or eight 
miles. A steep cone of detritus clings here and there 
beneath some channel of falling water on the sides; but 
for the most part the walls are grim and sheer. A sharp 
eye may sometimes detect old stream-levels on the higher 
portions of the cliffs, where the torrent formerly could 
undercut the wall or has drilled out a long-fronted and 
shallow cave ; but these levels have been long ago forsaken, 
and the canon is still in process of formation — it has not 
yet reached its greatest splendour. 

Its mouth opens on an expansion of the valley, with 
a green flat floor, eagerly seized on by the agricultural 
peasantry. The rocks here may be different in character 
from those hitherto traversed, and the torrent, sweeping 
from side to side, has been able to widen back the valley. 
Or side-streams may have indented the walls and brought 
down more material than could here be swept away. Clearly 
at some time the valley has been choked, and the work of 




68 OPEH-AIR STUDIES 

the ffiaifi stream hsm then been oonfiiied to spfreading ont 
the detritnM evenly. If, for inistanoey a taln&-fan, the broad 
end of »onie huge cone, has encroached npon it, the river 
has worked away at the base of it, and has laid out the 
material in level stretches across the floor. The tains and 
its fellows on either side have continued to slip forward, and 
the stream has risen upon the pebble-beds which it cannot 
sweep away. Dammed back occasionally by a slip of greater 
magnitude, it has overflowed its bounds and converted the 
expansion of the valley into a lake. The head of water 
thns produced has at last overcome the barrier, and the 
level pebble-banks, gently deposited during the lake-period, 
have become drained fairly dry, and have been finally covered 
with vegetation. The river is now seen wandering through 
them, as it did through the meadows of its gathering- 
ground ; and, as it cuts its way down again in a narrower 
ohatitiol, it becomes turned to one side or the other by any 
large block that bars its way. Its course is thus winding 
and uncertain, and it sometimes forms long loops and 
doublings, only to cut through finally by a more direct 
route, leaving its former curved bed desolate and dry. 

Huoh a grassy level, with the stream winding across it, 
is stylt^d an alluvial flat, and the material laid out by the 
river is known as the alluvium. The stream is frequently 
cutting away its bank on one side and depositing pebbles, 
the new alluvium, on the other, where some promontory or 
wliarp bend checks the flow. Hence the alluvium is always 
undorgoing redistribution, and is liable to be flooded over at 
any titne atid restored to a fairly uniform level. 

Such basins of alluvium, which are frequently the site 
of ancient and temporary lakes, are common along Alpine 
rivers. As we cross this one, we see the valley again con- 
tracting 5 the road drops more steeply, and enters a wilder 
country in a series of bold windings ; and soon we ore in a 
siH3ond goiye — we have left the area of arrested flow and of 
de|>osit4on n>r another one of rapid excavation. 

h\ this way, limited by a number of local accidents, the 
alluvial llat^^» witii villages clust.erod on them, and grim 
defilos» <H^hotng only the roai* of waterfalls, succeed one 
another in this active i>ortion of the river. In time we 
liiaU roodi «M\ aiva, s^>me 3000 feet or so below the sources 
ot tl\e «t40Minu wher^ tht^ flow is no longer sufficient to do 



DOWN THE VALLEY 69 

much in the way of excavation, and where ordinary atmos- 
pheric agents, rain and frost and wind, have had things 
mostly their own way. The valley becomes a more ordinary 
one ; that is, it has grown wider far more rapidly than it 
has been deepened. 

Here, then, the talus-cone will appear in its best de- 
velopment, stretching from the pebble-strewn floor of the 
valley backwards at a gentle angle towards the crags. If 
we look closely, the prominent features of the lower slopes 
will be seen to arise from the arrangement, and even from 
the overlapping, of these great detritsJ fans. In places they 
have become fairly consolidated; trees have grown upon 
them ; and the side-streams to which they owe their origin 
never in these days flood across the whole. By successive 
downpourings of boulders, the water has slowly raised itself, 
running upon the central line of the conical slope ; and then, 
in ordinary weather, it cuts little channels in the yielding 
material and tends to undo its work of deposition. But 
every now and then it rises fiercely and spreads new pebbles 
broadcast ; the old channels are obliterated, and, when the 
storm is over, a real addition has been made to the cone, 
a real step forward has been taken towards the ultimate 
destruction of the higher crags. 

The result of this uplifting of every torrent upon its own 
fan of detritus is that the villages in our valley are so situ- 
ated that we go uphill into them from either side. They 
had to plant themselves where they could get at the water, 
and there is consequently a wooden bridge in almost all of 
them, at about the highest point of the road across the cone. 
This is contrary to one's ideas about well-conducted streams, 
which usually run in valleys of their own, instead of on these 
broad and convex slopes. 

To secure the houses from being attacked, the stream 
has to be rigidly "corrected " ; but there are acres on either 
side of it which have a very fluctuating value. And the 
lowest part of the fan, though covered with a straggling fir- 
wood, is traversed by numerous branches of the stream, like 
the mouths of the Nile delta, and is thus practically useless 
for cultivation. Below stretches the waste of alluvial stone- 
banks and dwarf willows, with the main stream rushing 
aggressively in the midst of it, along its variable curves. 

This type of valley-side is continually presenting new 



i 



70 OPEN-AIR STUDIES 

problems to the peasant. The vast taluses, banked up one 
against the other, have no firm connexion with the rocky 
wall behind. The swirling action of the river at their base, 
or a few hours of rain, lubricating the pebbles and soaking 
far down within the mass, may upset their equilibrium and 
cause a widespread movement. Such landslides are so 
frequent that men are enrolled in every commune, whose 
duty it is to turn out and to help to reconstruct the roads. 

I was cycling with a friend one evening across the broad 
talus-heaps to the east of Imst, not far from Innsbruck. It 
was a wild summer, with thunderstorms every night amid 
deluges of August rain ; and one of these sudden downpours 
had just reached us. We were pushing on in the dusk 
through the rough and ragged woodland, where few of the 
trees enjoy suflBcient quiet to grow into a handsome middle- 
age. All at once we saw that the road had given way before 
us; the stones were moistened with the rain, the limestone 
dust between them being converted into mud ; and the hill- 
side was here in motion like an oozy river across our track. 
It was a striking sight, this steady flow of stones, into which 
we could have dipped our hands ; but our position, and that 
of our machines, were too insecure to allow us to stay long 
upon the brink. We retraced our route for some miles, 
noting at other points how suspicious yellow mud-flows were 
beginning to creep out across the roadway. Next morning 
we found that the material had come to rest, after cutting a 
groove in the more coherent portion of the slope and flowing 
down into the main valley of the Inn. 

To dwellers in these valleys such accidents are part of 
ordinary life; and the extensive areas of gently shelving 
ground that remain untouched by cultivation show how these 
lower slopes are continually liable to change. A map of such 
a country on a large scale, say i : 2S,CXX3, or two and a half 
inches to a mile, would be out of date after any stormy season. 

Landslides of fair magnitude may actually dam up the 
main stream, and may thus cause a rapid flooding of the 
higher portion of the valley. Such slides are common in the 
gorge of Lienz, the material coming down from the side- 
valleys into the narrow channel of the Drau ; and these 
heaps of detritus have to be cut through artificially, to check 
the formation of a lake which ultimately would overflow and 
burst out down the gorge. In former days, this excess of 



DOWN THE VALLEY 71 

supply over the means provided by Nature for carrying it 
away has choked many ravines, and has even formed per- 
manent and narrow lakes within them. More often the 
evidence points to the lake having burst through the barrier ; 
and the torrent has since reasserted itself, and has carved its 
channel easily down to its former level through the thickly 
accumulated alluvium of the lake. 

But remarkable changes may occur in the geography of 
so unstable a district, and that in a few hours, especially in 
areas where man is not on the alert. Let us imagine a pass 
in the mountains, where two rivers rise, one falling down an 
eastern, and the other down a western slope ; and let a side- 
stream enter the eastern river, close to the summit of the 
pass. A landslide from a neighbouring mountain may occur, 
and may cross the junction of the tributary and the main 
stream ; it may thus divert the former into the western river, 
providing a slope for it across the pass, and so profoundly 
altering the system of natural drainage. Such an event 
might easily have happened at Toblach, in central Tyrol. 
The river Rienz has already been invaded by taluses, which 
have formed the little Lake of Toblach ; and a great slide 
from the Sarlkofl might even now turn its waters eastward, 
and thus drain the Hohlenstein valley into the Black Sea 
instead of into the Adriatic. 

So we may fully recognise, as we before hinted, that 
maps of uncultivated countries, if we only make them large 
enough to show the details, are at least as often in need of 
rectification as the plans of rapidly growing towns. We said 
rightly that Nature was at work all round us. 

In these higher valleys, the changes wrought by ordinary 
landslides may be altogether surpassed by true landslips, 
which are often catastrophic in their scale. Records of terrific 
rock-falls are common in the history of Alpine villages ; as 
usual, the more magnificently developed the mountain-range, 
the more it is exposed to violent action, the more rapid are the 
phases of its decay. The rocks of a great chain, as we shall 
see in another chapter, are intensely folded one upon another, 
and hard layers may lie inclined upon softer ones at steep 
angles among the mountain-peaks. Enormous masses, once 
connected, become cut into fantastic forms by denudation, 
and finally may be undermined and may be rendered utterly 
unstable. From one cause or another, whole mountain- crests 




72 OPEN-AIR STUDIES 

may become loosened and detached; thus in one case an 
earthquake released the mass, in another the balance was 
disturbed by simple quarrying-operations at its base. Land- 
slides and landslips of course graduate into one another ; but 
the typical landslip is a thing that cannot easily be fore- 
seen, and that may result from centuries of stress among the 
folded masses of a mountain. 

It is diflScult for us to conceive in the British Isles the 
far-reaching effects of one of these huge rock-falls. As 
we said when we sat among the dSbris in our mountain- 
hollow, our own hills have got past the stage of violent 
catastrophes. The great landslip near Axmouth, in Devon- 
shire, which occurred in 1839, gives one some idea, however, 
of the changes that may be produced in a few hours. Sir 
Charles Lyell, in the later editions of his "Principles of 
Geology," has made us familiar with its details. At this 
part of our coast massive beds of chalk and sandstone rest 
upon clays, which slope outwards towards the sea. The 
permeable rocks allow water to soak down until it reaches 
the clay, where it lubricates, as it were, the natural inclined 
plane provided. On December 24, 1839, about a mile of 
the coast slipped seaward, producing great rents and fissures 
in the mass, and forcing up the broken material on the 
shore in front of it to form a ridge some forty feet in 
height. 

The east coast of County Antrim, from the occurrence 
of a precisely similar series of beds, is continually subject 
to small landslips, and at Garron Tower a mass of chalk, 
capped by basalt, nearly two miles in length, has sunk 100 
feet and more from the main plateau, owing to the yielding 
of its supports. 

In the Alps we have unfortunately too many records 
of landslips in the upland valleys. With very few excep- 
tions, they have occurred in the areas of stratified rocks, 
that is to say, where the rocks are disposed clearly in layers 
one upon the other.^ 

One of the most recent and most carefully studied 
instances is that of Elm, among the Alps of Glarus, which 
was reported on by Professor Heim. On September 11, 

* S«o Noiunayr, "Ueber BergstUrze/' Zeitachr. der deutsch u. obsterrcich. 
Al))cnv€rein8t Bd. xx (18S9); A. Irving, ** *Berg8turze' or * Laudslips,' " 
ChoL Mag.y 1883, p. 160. 



DOWN THE VALLEY 73 

1 88 1, a rock-slip descended from the Tschingelberg above 
the village, three falls occurring in twenty-one minutes. 
The debris came down like a waterfall, the enormous blocks 
leaping from terrace to terrace of the mountain, and finally 
rushing on like a flood over nearly level ground for about 
a mile. This river of stones even scaled a hill to which 
a number of the villagers had fled for safety, and it travelled 
in the valley-floor at the rate of thirty miles an hour. 

In 1806, a mile of the face of the Eossberg, a mountain 
at the south end of the Lake of Zug, fell into the valley 
between that lake and the Lake of Lowerz ; 457 persons 
perished, and the huge blocks of conglomerate were heaped 
across the pastures and the villages. At the present time 
the area is traversed by the St. Gotthard railway, and on 
all sides the sharply angled masses, as large as houses, can 
be seen scattered across the slopes, in a matrix of gravel 
and fine sand. The old rocky bosses in the valley have 
been swallowed up by the great flow of boulders, which 
have climbed the Inllocks and lie like perched blocks upon 
their summits. The bare crag of the Rossberg rises two 
miles away above this extraordinary and impressive land- 
scape. 

A similar scene of abrupt destruction is crossed by the 
high-road from Italy, as it ascends to Cortina in Southern 
Tyrol. The last great slip took place here in 18 14; and 
the road is at any time liable to be invaded by a further 
creep downwards of the debris. Both here and beneath the 
Rossberg, respectable little fir-trees have already planted 
themselves upon the boulders, and serve to emphasise the 
enormous size of the fallen masses. 

Professor Heim has also pointed out how the valley of 
the Vorder Rhein, from Ilanz to Reichenau, has been in- 
vaded in very early times by a landslip from the neighbour- 
hood of Flims. The detritus has formed hills 1800 feet 
high above the valley-floor, and the whole mass of this pre- 
historic fall is calculated as 15 cubic kilometres,^ or 1500 
times as great as that of Elm. In fact, a range equal in 
size to the Malvern Hills seems to have been abruptly 

^ A. Heim, " Der alte Bergsturz von Flims," JaJirb. des Schweizer Alpen- 
Hub, Bd. xviii (1883), p. 3CX) ; and Heim, "Geologic der Hochalpen zwischen 
Reuss u. Rhein," Beitrdge zar geol, Karte der Schweiz, Lieferung xxv (1891), 
p. 431, and pi. vii, fig. 6. 



74 OPEN-AIR STUDIES 

planted in the Rhine valley, as a mere incident of the long 
series of attacks which have been going on for ages, and which 
will ultimately destroy the Alps. 

It may be worth while to try and find some measure for 
the masses which are thus transferred in a few minutes from 
the crest of a mountain to its foot. Any visitor to Dublin 
is familiar with the bold promontory of Howth, which rises 
like an island on the north side of the bay. It is a pictur- 
esque feature, rising 560 feet above the sea, and is about two 
miles across in all directions. Its form makes it possible to 
calculate its mass above the sea-level with fair approxima- 
tion. Now the Elm landslip brought down io,cxx),CXX) cubic 
metres of rock, and ninety such falls would destroy the whole 
of Howth. Sixty landslips like the Rossberg would similarly 
remove it ; while the two great falls from the Diablerets in 
central Switzerland in the last century were together equal 
to yV^h of Howth. The prehistoric landslip of Flims, however, 
according to the figures of Professor Heim, would have re- 
moved seventeen Howths at a single blow. The mass of 
material brought down would, in fact, have built a causeway 
fifty- six miles long, half-a-mile wide, and 660 feet in height. 

The Isle of Wight, with its area of 1 55 square miles, may 
be expected to form a feature of our south coast fi'om this 
time on into far-distant epochs. But, were its rocks elevated 
into the perilous positions occupied by beds of the same age 
in the Alps, their existence would at once become endangered. 
The matter is brought home to us somewhat startlingly when 
we realise that the catastrophe of Flims would have carried 
away half the island. 

We have already seen how our typical Tyrolese valley is 
liable to be converted locally into a lake by landslides from 
the mountain- walls. A considerable and abrupt landslip may 
similarly dam up the river, and may even provide a permanent 
barrier. A fine example of this kind occurred in India, in 
September 1893, ^^ ^^^ neighbourhood of Srinagar.^ The 
rock-falls from a mountain above the village of Gohna con- 
tinued for three days, accompanied by clouds of white lime- 
stone dust, which spread for miles. Blocks, as at Elm, were 
projected for distances of a mile, and broke down trees 
across the valley. A wide dam of detritus, weighing, on Mr. 

* T. H. Holland, "Report on the Gohna Landslip, Garhwal, " iZcconfa 
Oeol, Surv. of IndiUf vol. xxvii, p. 55. 



DOWN THE VALLEY 



75 



Holland's estimate, 8oo,ocx>,CXX) tons, finally occupied the 
hollow, and converted the upper reaches into a lake three 
miles long and a mile and a quarter wide. 

Mr. Holland's prediction as to the date when this lake 
would overflow was verified almost to a day in August 1894. 
But the dam was destroyed more rapidly than he anticipated, 
and the whole body of water escaped in some two hours** 
The geological effects of this flood, moving at twenty-four 
miles an hour and rising 2CX) feet in some parts of the 
valley, will probably be a valuable lesson in the distribution 
of stones and boulders. 

Our contemplation of the huge unstable taluses, and of 
the old rock-scars above them, must now for the time come 
to an end ; we must 
move farther down 
into another region 
of our valley. Here 
the floor is flat, and 
is used for smiling 
meadows; but the 
walls on either hand 
come down verti- 
cally, in striking 
contrast, and there 
seems no relation 
between the sides 
and the bottom of 
the valley. 

We stand at the 
foot of one of these great cliffs, and look across at the oppo- 
site one a mile or more away. We have here something like 
the gorges of the higher regions, only on a somewhat bolder 
scale ; but the area from cliff to cliff has been filled in with 
alluvial pebbles (fig. 4). It is a portion of the valley where 
deposition has, for a long time, been in excess of excavation ; 
too much detritus has been cast into the stream. 

It may be that landslides and stormy seasons aided in 
the choking of the valley ; and the stream may now be cut- 
ting its way down again, swiftly and dangerously, between 
cliffs of loose alluvium. The valley of Aosta on the south 
side of the Alps shows us banks of pebbles now cut through 

* Nature,, vol. 1, p. 501. 




Fig. 4.— Section of Qorqb cuokbd with 
Alluvium. 

A, alluvium ; s, the subsequent groove formed 
by the stream ; T, a talus or detrital cone, which 
has grown out over the alluvium. 




76 OPEN-AIR STUDIES 

in this way, and the railway-engineers experienced curious 
difficulties in making their artificial cuttings. Some of these 
had to be roofed over and converted into tunnels, to prevent 
the constant sUpping in of the sides. In the case of rapid 
streams, the banks are always changing, and short work 
will be made of the alluvial flat if artificial checks are not 
resorted to. 

Sections in the alluvial infilling of our valley will give us 
an insight into the work of the river as an accumulator ; and it 
will be well to find our way down one of the steep zig-zag paths 
to a little bridge, from which we can view both banks. The 
pebbles are not thrown down without method or arrangement, 
as they might be in the products of a landslide which has 
come to rest. On the contrary, a distinct grouping in beds or 
layers is visible (Plate III). Here a coarse mass of boulders 
lies heaped together, the rounded blocks sticking out con- 
spicuously on the steep bank above us, like skulls in a giants' 
graveyard. But below them the pebbles lie with their longer 
diameters generally horizontal, as they would if one took a 
heap of them and smoothed it out on a flat table with the 
hand ; the water in this case has acted as the hand, and has, 
in swaying them this way and that, finally formed a layer of 
them, which we technically term a Stratum. The plural of 
this word is strata, and when we say a rock is stratified, we 
mean that natural agents have deposited its constituents in 
a series of strata one upon the other. 

Beneath the stratum of pebbles comes one of sand, with 
a few small stones scattered through it. When this was 
formed, a quantity of finer material, perhaps a muddy and 
sandy flow from some side-valley, was being brought into 
the higher reaches of the stream. Or the stream itself 
became checked in its flow by alterations in its course or in 
the form of the valley-floor above, and could no longer carry 
along the larger stones. So it merely brought away the finer 
sand, with a few little pebbles, and for a time made beds out 
of these, as if there were no coarse materials up the valley. 
We shall see later, in observations at the river-mouth, how 
far this process of natural sifting may be carried. 

If we examine the coarser strata in this section of the 
alluvium, we shall find the sand there also ; but it is dis- 
tributed between and over the surfaces of the stones, which 
are far more conspicuous. Under the bridge some one has 



kT*^^^ 


1. V.-:'-^*-!— 


.-^-^^ 


i: 








- '- "N^ 


3 





STRATIFIED SANDS AND GR.WELS, 
Showing Fine and Coaksb Materials. Antrim. 

Platb III,] f AslDgra^lud lij ^\i. ^'Msuivi. 



DOWN THE VALLEY Ty 

confidingly left one of the shallow wooden pails which are 
used for carrying water or milk, or for washing clothes, 
throughout this mountain district. If we borrow it, and 
throw some of the material from a coarse-grained stratum 
into it, we can imitate the final separating action of the 
stream. Let us fill up the pail with water and shake it 
briskly from side to side. If we pour the contents out 
quickly, the rush of water will carry with it pebbles and 
sand and mud alike, and we reproduce the action of the 
river when it formed the original stratum. But if we deal 
more gently, we find the top layers of the water becoming 
thick with the mud and sand, among which, if the sun is 
shining, we can see a number of tiny flakes of mica gleaming ; 
and now we can pour off this finer material and leave the 
coarser and more unwieldy stones behind in the bottom of 
the pail. The particles of sand and mud and fine mica have 
probably quite as high a specific gravity as the stones that 
remain behind ; but they offer so large a surface in propor- 
tion to their mass that they are easily washed about in the 
water and become poured off with it. 

We have now imitated the action of the river when its 
current is more gentle, and when it begins to sift apart the 
alluvial materials for redistribution in the lower part of its 
course. We may even go further, and by careful washing, 
and by allowing the disturbed material to stand for a short 
time, we may find that the sand will settle, while the finest 
mud can be poured off. Then we can, as a second stage, wash 
away the sand, leaving only the coarser pebbles ; and thus we 
may, like the river in some places, produce a triple separation. 

The layer-structure, which we call the stratification^ is 
not very regular in these rough materials, and no one stratum 
extends for any long distance in the section shown us in the 
bank. The beds of finer sand lie on one another, sloping in 
various directions, a certain number being deposited by a 
current swirling one way, and then others following under 
the influence of a different movement of the stream. Such 
a structure, where the beds do not all slope one way, is 
known as current-bedding. This irregular stratification is 
further disturbed by the pressure of coarse boulders, which 
become rolled down in exceptional seasons; and the group 
of blocks sticking out above us proves how very variable 
is the action of a mountain-stream. 




78 OPEN-AIR STUDIES 

When a great bank of snch detritus has been exposed for 
a long time to rain and weathering, gullies are cut in it by 
the storm-rills from above, and these vertical grooves become 
rapidly deepened. But the larger blocks serve to protect 
the portions immediately below them from denuding action, 
and conical pillars result, carved out by rain, some excep- 
tionally large stone forming a cap at the summit of each. 
These tall cones can be seen on any hillside where banks of 
old detritus have been subsequently excavated into cliffs; 
GlencuUen, near Dublin, contains fair examples of these 
earth-pyramids, and the soil at the bottom of any hedge, 
when examined after a shower, will show the same feature 
pleasantly in miniature. 

The more we remain in the bottom of the present 
stream-cut, beneath these walls of loose pebbly alluvium, 
which perhaps rise lOO feet above us, the more we shall 
believe in the carrying power of the torrent. Its action is 
so violent that even the hardest rocks are converted into 
smooth round pebbles by friction one against another ; and 
Professor Bonney ^ has told us that 3000 feet of descent in 
the upper reaches of an Alpine stream is suflBcient to round 
pebbles of ordinary hard rocks, such as granite. As we 
noted upon the mountain-slope in our own islands, the 
smaller materials become more slowly rounded than the 
coarser, owing to their being buoyed up and kept apart by 
the flowing water. A stream travelling at four miles an 
hour at the bottom of its bed can move forward pebbles 
nine inches in diameter, and two-inch pebbles can be moved 
by a flow at the bottom of only two miles an hour. 

The steep slopes of the stream-beds in the upper region, 
the region of excavation, greatly assist the rapid denudation 
of the valley-head. A Bulgarian student, M. Baeff of 
Shipka,^ has recently given us some interesting results of 
a year's observation of the Arve, one of the most striking 
torrents of the Alps. He finds that the solid material 
brought down by this river in suspension is greatly increased 
by only a slight increase in the volume of the water, while 
the matter carried invisibly in solution is much less variable 
in amount. The level of the river is highest in summer, 
which is likely to be true of any stream resulting from the 

' "The Rounding of Pebbles by Alpine Rivers," Qeol, Mag., 1888, p. 60. 
2 " Les Eaux de TArve ; " Greneva, 1891. 



DOWN THE VALLEY 79 

melting of snow and glacier-ice ; and any increase in volume 
of a stream upon a steep slope means a great increase in 
its velocity and its power of transporting pebbles. The 
total quantity of material removed, both in suspension and 
solution, from the mountains of Savoy by the Arve during 
the year 1890 was found to be 965,457 English tons, a 
very considerable figure when we remember that this action 
is continuous. This is, of course, a true torrent, the Arve 
of Shelley — 

" Where power in likeness of the Arve comes down, 
From tne ice-gulfs that gird his secret throne. 
Bursting through these dark mountains like the flame 
Of lightning through the tempest." 

But the denuding work of rivers may be appreciated 
when we remember that an almost equal amount of material 
is brought down annually by the Thames. In this case. 




Se^ fere/ 

FiQ. 5.— Section showing a Slope op i in 17. 

however, the great bulk is carried in solution from the ex- 
tensive tracts of limestone over which the river flows. 

The actual fall of the Eiver Arve in the first twenty-eight 
kilometres of its course, through the Valley of Chamonix 
from the ridges of Mont Blanc, is 1700 metres, or i in 17^ 
(fig. 5), the steepest slope that an ordinary railway train 
can climb being about i in 38. If we take an example 
from the mountain -streams in our own islands, say the 
River Liffey as it descends from the moorland down into 
the county of Kildare, we find that it has a fall in the same 
distance of only 336 metres, or i in 83. The Rhine, again, 
as an example of a long river, with its course of 760 miles, 
falls on an average 10 feet per mile ; but in the mountain- 
ous part of its course, from the glaciers on the Bernardino, 

^ That is, if we measure oflf 17 metres, or kilometres, or feet, or inches, 
along the river's course upon a map, in that distance the floor of the valley 
has approached i metre, or kilometre, or foot, or inch — according to the 
unit selected — towards the level of the sea. 



8o OPEN-AIR STUDIES 

through the alluvial fields of Spliigen, and down the ravine 
of the Via Mala, it falls 200 feet a mile, or i in 26. Prom 
B§,le to its mouth, on the other hand, it descends only about 
1.6 feet per mile, or i in 3333. 

But no mere comparisons can give us the true effect 
of our Alpine torrent, as it comes down in Tyrol uncon- 
taminated by glacier-mud, clear and green and swirling, 
rejoicing like a giant to run its course. like most good 
things of the world, it compels us to go forth and visit it, if 
we would grasp its meaning thoroughly. Soon, however, we 
shall see it in another phase, laying down its burden and 
spreading itself out in lazy shallows, as we reach the gentler 
and more shelving portion of the valley. 

Here, for instance, is a long stretch of alluvium, where 
the river is now powerless to do more than redistribute the 
detritus during occasional floods. The sheer sides of the 
valley show that in former ages cutting action was predomi- 
nant ; but the gorge is now choked, the gathering-ground of 
the torrent has been lowered too far by denudation, and the 
period of deposition has finally set in. The story of all 
streams is alike — excavation at one end and deposition at 
the other ; and the area of deposition extends slowly back 
up the valley as time goes on. 

The Rhine, between Ohur and the Lake of Constanz in 
eastern Switzerland, shows the alluvial stage very strikingly. 
Old stone causeways have been discovered some 15 feet below 
the present surface of the valley -floor; and the cliffs at 
Hohenems and elsewhere drop sheer into the alluvium, show- 
ing the former gorge-like character of the valley. The river 
and its tributaries have brought down so much material that 
the whole course of the water has been changed by the de- 
trital banks. In prehistoric times the Rhine flowed past the 
site of Sargans, and away through a narrow valley which it 
had cut for itself to the north-west. The Lakes of Walen and 
Zurich occupy part of this old course of the Rhine ; but the 
streams flowing from Sargans into the gloomy hollow of the 
Lake of Walen are now very trifling in their volume. By slight 
shiftings of its alluvium, the Rhine has banked itself out of 
the ravine of the Lake of Walen, and has crossed northward 
into another valley leading down into the Lake of Constanz. 
The relations of these two valleys can be seen in any good 
atlas ; and the levels around Sargans are such that it would 



DOWN THE VALLEY 8t 

require no great feat of engineering, the cutting of a barrier 
only fifteen feet in height, to turn the river again into the 
deserted gorge of Walen.^ 

Little hills, which have escaped complete burial, stand 
out above the general flatness of the Bhine-alluvium ; but on 
the whole the floor of the present valley is in singular con- 
trast to its sides. The 111 comes in at Feldkirch, bringing 
down pebbles from the Arlberg Pass ; and it shoots out from 
a fierce little gorge into a great alluvial level four miles wide. 
Kfteen miles north of this the Lake of Constanz opens, and 
arms of detritus are being thrust out into it, and threaten in 
time to cut off the port of Eorschach from Lindau. 

Wherever a lake, indeed, occurs, from one cause or 
another, in the valley of a mountain-stream, it tends to check 
the flow and to cause a deposition of the material that is 
carried in suspension. The lake becomes shallower, banks 
of mud and sand are to be seen beneath its waters, and little 
reedy islands spring up around the mouth of the main stream. 
The mouth itself, like that of the Ehine at Eheineck, may 
become fringed with alluvial banks, which run out like flat 
breakwaters on either side of its course into the lake. The 
water washes through these occasionally, and a number of 
small mouths may arise round about the main one. The 
general alluvial deposit forms a very -shallow cone, like an 
exceedingly flat fan-talus, its apex lying up the valley and 
its broad end spreading into the lake. Such a deposit is 
known as a Delta, from the resemblance of its form to the 
Greek letter A. In smaller lakes, like the Toblachersee of 
Tyrol, the mode of origin of deltas can be very clearly studied ; 
and in our own islands, as at the Upper Lake of Glendalough, 
in Wicklow, we can often look down from the heights into 
some black tarn below, and see the grassy alluvium above 
the upper end stretching on continuously under the water 
in brown and sandy shallows. 

In time these lakes become completely filled up, and an 
elliptical alluvial flat results, covered with vegetation, through 
which the river winds. Such vanished lakes, not drained by 
some catastrophe like the bursting of the Gohna dam, but 
simply abolished by alluvial action, may be detected again 
and again in our wanderings, if we continue to cultivate an 
eye for varying fonns of surface. 

* See KecluB, " Nouvelle Gdographie universelle," tome iii, pp. 55 and 60. 

F 



82 OPEN-AIR STUDIES 

If we still follow our lyrolese river down east to the 
country of the plains, we find the signs of deposition increas- 
ing, the signs of cutting-action rare. Soon, perhaps among 
the woodlands of Styria, the river becomes navigable for 
pine-rafts, which go swirling down upon its full broad sur- 
face, the men sti'aining at long oars to guide them round the 
rapid bends. And finally the hills about us sink down under 
long waves of golden corn-land, which stretch eastward in a 
still hot midland haze ; small villages of one-storied houses 
lie scattered among the fields, connected by irregular and 
dusty roads. Far away there is a dull panting sound, and we 
may see a drift of smoke out there across the level sun- 
light. It is the Danube steamer, journeying southward to 
Belgrade. 

At this point it is well to look back, and to consider the 
action of our river as a whole. Clearly, it has carved out its 
own valley, just as the little storm-torrents carve out their 
grooves ten or twenty feet deep in the loose soils of a hill- 
side (p. 29). The form of the sides of the valley depends 
upon a number of circumstances, many of which we have 
noticed as we wandered through it. The beautiful promon- 
^ tories, seen shading off one behind the other, with approxi- 
mately the same outlines, as we look up towards the valley 
head, are really parts of the great wall formed by the action 
of the river, the hollows and combes between them being 
cut back where tributaries come down from the sides. The 
general form of the walls, where the rain and the river work 
together, shows a steep slope in the neighbourhood of the 
stream, then a more gently shelving region, on which the 
summer ch§.lets stand among the grassy " alps," and finally 
the region of the upper rocks, where frost-action assists the 
driving rain-storms in maintaining a rugged and pinnacled 
wall of crags. A section (fig. 6), accurately drawn to scale, 
across one of the steepest pieces of scenery in our islands, 
will show the general outlines well. The steepest valley- 
side is here 40°, and others reach as much as 35°, an ordi- 
nary stiff slope being about 30°. In the centre we have the 
crag of Sgurr Fhuaran, one of the great masses in the west 
of Koss-shire, 3505 feet above the sea, or about the height 
of Snowdon. On its left is the hollow of Glen Shiel, and on 
its right, across another glen, we see the broad back of 
Beinn Fhada. The construction of such sections, from the 



DOWN THE VALLEY 



83 




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84 OPEN-AIR STUDIES 

contoured maps issued by various governments, is always a 
useful lesson in physical geography. 

Above this, also in fig. 6, we have drawn, to the same 
scale, a section across one of the most impressive valleys in 
Europe, the Val de TAU^e Blanche, on the south side of 
Mont Blanc. The spurs of the gigantic mountain are set 
with startling granite pinnacles, or aiguilles; but in this 
section we have passed down a less broken portion of the 
slope, and have secured the general curve of the valley-side. 
The highest point on the left is the summit of Mont Blanc, 
15,730 feet above the sea ; the same sea-level line is used as 
for the Scotch section below. The dome of snow at the 
summit ends abruptly in a craggy descent to the gathering- 
ground of the Glacier du Bromllard. We then descend a 
very steep slope beside the glacier, which melts away shortly 
before we reach the valley. The floor of the valley is occu- 
pied by the moraine-covered Glacier de Miage, after which 
we climb a rocky slope and pass along the arete of Mont 
Berio Blanc. Yet the curves of this wild and magnificent 
landscape show a remarkable resemblance to those of Sgurr 
Fhuaran and Beinn Fhada ; the difference is, after all, one 
of scale rather than of form. 

When we speak of rivers performing so much cutting- 
action in proportion to the slope on which they run, it is 
clear that some sort of slope must have existed before the 
river began to run. The course of a stream is primarily 
determined by the occurrence of a watershed, a region 
elevated, slightly or greatly, above the sea, and sloping 
down towards it on either side. Water condensed out of 
the atmosphere on the watershed must flow down one slope 
or the other ; and there may be either a boggy upland along 
the summit, or a mere knife-edge of jagged rock. You may 
sit, for instance, on the ridge of Le Chenaillet, on the fron- 
tier of France and Italy, and kick stones with one foot into 
the waters that feed the Adriatic, and with the other into 
those flowing to the Golfe du Lion. Or you may look 
down from a knoll in the forests of North-East Bavaria 
into three great river-systems — the Elbe on one hand, 
wandering through Bohemia; the Main on the other, a 
mere affluent of the lordly Rhine; and in the south the 
hollow of the Danube, already a considerable stream, with 
1400 miles yet to run to its delta in the Russian seas. 



DOWN THE VALLEY 85 

The watershed once determined, the rivers pick out the 
lines of greatest steepness ; but other circumstances, such 
as the arrangement of hard strata against soft ones, the 
folds of the strata themselves, or the direction of the prin- 
cipal joints, come in to modify their course.^ Soon the 
slopes become cut into by a series of main valleys, which are 
joined by lateral ones, branching like the subdivisions of a 
fern-leaf ; and the drainage-system of the country is set up 
along these well-defined grooves. The action of the torrents 
and waterfalls of the steeper regions is to cut back the head 
of the valley; and, as this goes on on both sides of the 
watershed, two valleys finally meet at their heads and form 
a notch in the mountain-ridge. Such a depression in the 
main ridge is called by mountaineers a col, and forms a 
pass, or place of passage, for those adventurous persons who 
prefer to see the world from both sides. 

By this cutting back of a valley-head, the river may 
come in time to look as if it had originally risen on the 
farther side of the watershed and had forced its way across 
it.2 It may even draw ofi* into itself the tributaries that 
formerly flowed into an opposite river-system ; it is only a 
question of one river cutting back its gathering-ground at a 
quicker rate than its rival on the other side of the pass. 

Other river-systems open up more serious considerations, 
which can only be answered during one of our later journeys. 
When we find in any district the channels of the waters 
passing right across the ridges of the hills, from some source 
far upon the other side, it becomes a question as to which 
were in existence first, the rivers or the hills themselves. 
The fact that mountains may be very modem features will 
perhaps be impressed upon us when we retara some day 
and examine their internal structure. Meanwhile, if we 
look round about us in a summer holiday in our own islands, 
we shall notice in the course of any upland river the essential 
features that we have studied in the Eastern Alps. On a 
grassy col, with the brown foot-track wandering across it, 
and the clouds driving up now and again from the hollows 
before a western wind, we may see the gathering-ground of 

1 For a discussion of the effects of earth -structure on the course of the 
River Drau, see Suess, ** Antlitz der Erde," Band i. p. 339. 

2 Of. R. D. Oldham, "The River- Valleys of the Himalayas," Journ. 
Manchester Oeogr. Soc. (1894). 



86 OPEN-AIK STUDIES 

the streamlets, and the black pools of the bog-land drain- 
ing out on this side and on that, one set of waters going, 
perhaps, to the Irish Channel and the other to the Grerman 
Ocean. We may follow down the watercourses through 
their torrentnsti^ to spots where they are checked by 
rocky barriers and deposit their alluvium ; and here we are 
likely to find walls and buildings, the outposts of the highest 
farms. We may come across valleys, like Glencullen in 
County Wicklow, once choked with gravel, and now again 
being cleared out by the stream ; and in the lakes and on 
the lower broader slopes we may see the formation of deltas 
and shallow terminal fans. 

Now and then we may even have excellent models of all 
these things in a few yaids of slimy shore. The clay-beds 
on the east and west coasts of the Isle of Wight, and, still 
better, the foot of the cliffs at Cromer, show one in miniature 
most of the features of river-erosion and deposition. The 
rain-showers, or the little springs, cut channels in the 
soft materials, and form fans of the suspended matter on 
the shore. On the surface of these fans the tiny river 
divides and ramifies, in imitation of the great cUbris-cones 
of Tyrol. An enterprising child with a spade can soon pro- 
duce a shallow lake, and can observe how it becomes filled 
and obliterated by the encroachment of a delta at its upper 
end. After storms, and often without adequate warning, 
mud-flows come down the channels excavated by the rills ; 
and thus even the more catastrophic features, the very land- 
slides of the Alps, are reproduced on a convenient scale 
before our eyes. 



CHAPTER IV 

ALONG THE SHORE 

It is a fresh morning on the shore, with a light breeze blow^ 
ing landwards, and the sun marking the broad blue band of 
open water beyond the shadow of the cliffs, and the white 
gulls sweeping far away to sea. Right and left the rocks 
run outwards, with a mile of bay between ; and a little river 
comes down on the left side of the curve, its mouth now 
deepened and walled in so as to serve as a harbour for the 
boats. On the same side the cliffs are fairly low, and a 
fishing-village clusters on them, its successive tiers of white 
houses being connected by steep lanes and flights of steps. 
The coast-guard station, with a well-kept lawn before it, and 
a signal-gun set neatly in the middle, stands on the plateau 
which forms the summit of the cliff. 

On the right, however, the landscape has a sterner air. 
A bold headland runs out to sea, vdth rocky islets at its base. 
The cliff rises some 7CX) feet from the water, and no sign of 
a landing-place is visible. The wild-birds have it all their 
own way there, and even the coasting-steamers do not dis- 
turb them, passing as they do outside the farthest islet. A 
white lighthouse, gleaming this morning in the sun, is planted 
on that outlying rock to mark the dangers of the channel. 

Looking again towards the little harbour, we see that one 
or two buoys and beacons are set about the river-mouth, as if 
the entry was not plain sailing ; and we may learn that a 
certain amount of dredging is resorted to, in order to keep 
the passage clear. Here, in the compass of this mile of bay, 
we have half the problems of the shore-line of a continent 
and the sea. 

The river, though it is not strong enough to roll along 
great pebbles, brings down a quantity of sand and mud from 
the inland country, and has been known to be quite thick 
and turbulent after heavy rains. At present it looks quiet 

enough, and we can see the usual deposit of broken china 

87 



88 OPEN-AIR STUDIES 

and gleaming meat-tins lying in the bottom of it under the 
lowest tier of houses. 

However, it has now and then scoured all this out, and 
cut alarmingly into the j)ebbly bank, and has even exposed 
the hard rocks which crop out in ribs farther down the shore. 
The materials of the floor were freely carried out to sea, to 
be added there to the growing banks beyond the harbour. 
Then came a time of gentler deposition, when mud covered 
up the floor again, and so brought things to their present 
and more comfortable condition. 

So this stream goes on forming its delta, where the 
current is checked on meeting the broad waters of the sea. 
Moreover, the deposition of material carried in suspension 
goes on more rapidly in the mixture of salt water and river- 
water than it would in the fresh water alone. It is a pretty 
experiment to take two tall glass vessels, and to fill one with 
fresh water and the other with water of about the degree of 
saltness of the ocean. Then pour into each equal quantities 
of fine dried clay, and stir the mixture thoroughly. In a few 
hours the salt water will be seen to be markedly clearer than 
the fresh water, the material in the former case having 
fallen far more rapidly to the bottom. Hence substances 
brought in suspension from the land are deposited close to 
the shores, and are only slowly sifted out farther by the 
action of the lower currents of the ocean (p. icx)). 

It is no wonder, then, that deltas in many places, despite 
the wash of waves on their outer rim, grow steadily forward 
from the shore ; thus, at the wonderful mouth of the Missis- 
sippi, the river runs out between banks of its own, as far as 
some sixty miles from the ordinary alluvial coast-line. The 
delta of the Ganges pushes itself southward in some fourteen 
or fifteen tongues, with a total width of about i8o miles; 
and the Danube similarly makes an encroachiug delta at the 
southern angle of Bou mania, the apex of the A being fifty 
miles inland, and the seaward front curving forward in the 
semicircle typical of such deposits. 

It is diflSicult to say how much of Venetia would be left 
if we were to wash away the deltas of the Alpine streams 
descending from the north, to say nothing of the enormous 
deposits of the Po. As we run from Mestre to Venice, the 
country is scarcely pure land or sea; we are on the very 
fringe of the alluvium, and the growing banks and islets are 



ALONG THE SHORE 89 

being covered with vegetation, which serves to bind them 
together, and to promote further deposits when the 
water brings sand against the plant-stems. It is a strange 
and melancholy landscape; and we soon realise how the 
lagoon of Venice itself has been cut off by alluvial barriers 
from the Adriatic. All these deltas, like our miniature one 
in the fishing-harbour, grow most rapidly seaward in times 
of flood and rainy seasons. 

The rate at which deltas grow deserves careful con- 
sideration, but its determination is beset with many diflSi- 
culties. When spread over a broad surface, the annual 
addition to the deposit does not seem particularly thick ; 
and a general survey of the great deltas of the world shows 
that hundreds of years are required for the deposition of 
a foot of strata. But such soft materials are continually 
slipping seawards, and are easily weighed down and rendered 
more compact by any new layer placed upon them ; so that 
a great addition may be made to them without the level 
of the general surface rising appreciably higher above the 
sea. Borings in the delta, such as have been made in sink- 
ing wells in Egypt, will, however, reveal the total thickness 
of the deposit, the earlier layers of which, essentially fresh- 
water in origin, have sunk far below the level of the sea. 

In our bay the tide has now turned, and the boats inside 
the harbour are already beginning to heel over. In an hour 
or two the space between the stone breakwaters will be 
almost dry, except for the stream, which we can then see 
wandering in the floor. Farther out, brown-pink sand- 
banks are beginning to appear, the result of the sea's 
action in throwing back the alluvium towards the shore. 
These banks, full of land-detritus, and even in part made 
of the old tins, and broken china, and so forth, carried out 
in times of flood, are a portion of the true delta of the river. 
They will be found mapped upon the Admiralty chart, 
stretching seaward as long tongues and islands, with the 
straight artificial channel cut in the midst of them, marked 
by its buoys and beacons. 

Doubtless a part of these sandbanks results from the 
material brought along the coast by the currents of the 
sea itself. The river-delta has only to thrust out an arm 
which will obstruct the free sweep of the waters, and tons 
of foreign sand and pebbles will be quickly planted down 




90 OPEN-AIR STUDIES 

against it. This is a matter into which we shall examine 
later, when we have climbed along the headland at the 
other extremity of the bay. 

Almost all rivers have their bars, produced by the 
deposition of material from the land on the one hand, and 
its rejection by the sea on the other. A barrier of pebbles 
and other detritus is formed across the mouth of the stream, 
and is often impassable for boats unless the tide is high. 

All these banks and barriers, in which both the river 
and the sea have played a part, come under the head of 
estuarine deposits. Sometimes the fresh water prevails 
against the sea, and true river-strata are laid down ; these 
beds, like the deltas formed in lakes, are called fluviatile 
deposits, those formed by the sea itself being styled 
marine. In the one series, the shells of animals that live 
in fresh water will be found, to prove the mode of origin 
of the strata ; in the other series, marine remains, seaweeds, 
&c., will be embedded. In any estuary, leaves, and twigs, 
and even large trees, will be washed down from the land, 
and will become covered up and preserved in both the 
marine and the fluviatile deposits. 

So far we have considered only the material brought 
down by our little river in suspension; but we may be 
sure that its waters contain a good many chemical sub- 
stances in solution. If we boil off a filtered sample of the 
water in a clean test-tube over a spirit-lamp or a gas-burner, 
we shall obtain these dissolved substances, which are left 
behind as a white or creamy film clinging to the bottom 
of the tube. Probably calcium carbonate is present in 
the greatest proportion, while combinations of magnesium, 
sodium, potassium, iron, &c., will also occur, including 
common salt, or sodium chloride. 

Now all these dissolved materials pass through the sand- 
banks, and over the bar, into the great sea unaltered. Some 
are laid hold of by those unconscious analytical chemists, 
the fishes and the molluscs and the sea-urchins, and other 
living creatures that abound in the waters, and are ex- 
tracted by them to form their skeletons and shells and 
strengthening plates ; others simply go on accumulating in 
the sea, which is salt accordingly, and is not fresh like the 
water when it first descends from off the hills. 

The "fresh" water of rivers is of course salt in some 



ALONG THE SHORE 



91 



degree, but so slightly that we do not notice any taste in it. 
It is only because of the great gathering of chemical salts 
in the sea that we find it has a characteristic taste, which 
is chiefly due to sodium chloride. This substance occurs in 
ordinary rivers in the proportion of about .0035 per cent, 
of any given weight of the filtered water, i.e., of the water 
with the suspended substances removed from it ; but in the 
sea it forms 2.8 per cent, of the weight. The total salts 
dissolved in river-water may equal .04 per cent, by weight ; 
but in the sea they may be as much as 3.5 per cent.^ 

If we evaporate off the water, and weigh out 100 
grammes of the mixed salts that remain, the proportions 
of these are found to be as follows : ^ — 



Sodium chloride . 
Magnesium chloride 
Magnesium sulphate 
Calcium sulphate 
Potassium chloride 
Other substances, including calcium car- 
bonate and silica 



Per Cent 
78.32 

9.44 
6.40 

3.94 
1.69 

0.21 

100.00 



We must remember that the oceans may have been salt 
from the time of their first formation on the globe ; but 
their saltness must have been largely increased by the 
enormous amount of material steadily brought down in 
solution from the land. The air is continually absorbing 
pure water by evaporation from the surface of the sea, and 
the layer from which this water is withdrawn becomes in 
consequence more highly charged with salts. Salt water 
has a higher specific gravity than pure water; and hence 
the surface-layers are constantly sinking, while other water 
of less specific gravity rises from below. This process, by 
itself, keeps up a slow circulation in the waters of the ocean. 
Bain, on the other hand, forms a layer of fresh water on 
the surface of the sea, which floats there until gradually 
mingled with the salt layers below. 

Near the mouths of great rivers the sea -water is 
naturally less salt than in the open ocean; and seas with 



^ See, for example, the analyses given in Huxley's " Physiography," pp. 
125 and 128. - Kriiinmel, "Der Ozean," p 94. 




92 OPEN-AIR STUDIES 

narrow communications with the ocean become practically 
like great lakes, and are far fresher than the average. Thus 
the northern waters of the Gulf of Bothnia contain only 
from .10 to .15 per cent, of salts, a figure increasing south- 
wards and westwards to .86, 1.65 (at Kiel), 1.9, and finally 
3 per cent, in the Skagerrak. Outside, in the North Sea, 
we have 3.3 per cent.^ Sea-water with 3.5 per cent, of salts 
has a specific gravity of 1.027. 

We have as yet left out of count the air dissolved in 
sea-water. This is caught in among the dashing waves, or 
is brought down by the rain, and allows the living creatures 
of the deep to obtain oxygen for their breathing. In the 
upper layers of the sea, at all events, the volume of oxygen 
absorbed is to that of the nitrogen as 35 is to 65 (see also 
p. 40). Air occurs, owing to the circulation of the ocean- 
waters, included even in the greatest depths of the sea ; and 
the colder the water, the more air is it likely to contain. 

If we wait until the tide again turns, and the line of 
foam, where the waves break upon the sandbanks, draws 
nearer and nearer to the shore, we shall be able to watch 
the work of the sea against the dark headland on our right. 
As we walk across to it, over the loose and rolling shingle, 
the dull boom, as of a distant gun, comes to us already. 
The water has reached the farther points of rock, and is 
bursting upon these obstacles with a shock at every line of 
rollers; and, before we hear each sound, we can see the 
spray rising in sudden clouds into the sunlit air across 
the bay. 

If we hurry on, we shall find those outlying rocks not yet 
surrounded by the water. We come under the shadow of the 
enormous cliff, and clamber over great angular blocks that 
have fallen from it. Then we reach ribs of rock running out 
seaward (Plate IV), with a little sand caught here and there 
between them. Red sea-anemones lie, like lumps of jelly, in 
the pools, and parts of the rocks above the level of low water 
are covered with close-set barnacles and limpets and peri- 
winkles, which are thus left dry twice a day. And so we 
come to the pinnacles and bluffs of rock that will soon form 
islands at high tide. 

These sea-Stacks looked small when we were over there 
in the harbour, for above them rose the frowning greatness 

* Krummel, " Der Ozean," p. 97. 



ALONG THE SHORE 93 

of the cliff. But they really are a hundred feet or so in 
height, and are composed of stratified rocks, of materials 
disposed in layers, like those forming the base of the cliff 
itself. The beds are tilted up in places, like a pile of books 
that has been thrust over sideways ; and the upturned edges 
form ribs and ridges when worn down to the level of the 
shore. Such ribs we have already noticed on our way out. 

The great waves are now nearing us in force, breaking on 
the seaward face of the stacks and booming in their crevices 
and caves. Let us climb up the ledges of the rock above us 
and look over towards the sea. 

The summit is fairly smooth, like a sloping table, being 
formed by the surface of one of the gently tilted strata ; and 
across it runs a huge cleft, down which we can look to the 
very l^ase of the sea-stack. On a ledge in the half-darkness, 
higher than the ordinary spray, a few sea-loving ferns have 
clustered ; and one or two tufts of grass have actually estab- 
lished themselves on the inclined table on which we stand. 

As we look down, there is a sudden swirl and rush below 
us. A roller has just burst on the sea-front, and the crest of 
the wave has fallen, and has flowed on like a torrent into the 
cleft. Its foaming edge laps into every seam and crevice ; 
the tongue of water breaks on the closed end of the cleft, 
and springs towards us in a cloud of angry spray. The roar 
of it spreads far across the bay ; it was this sound that we 
heard as we left the harbour. Then the water drains out 
again, for the tide is not yet high enough to keep the floor of 
the hollow full ; and we hear a grinding sound, as the pebbles 
down there are being dragged seaward one against the other. 

From one of the ledges below us the water flows out even 
after the floor is again left bare ; clearly some hollow must 
have been carved out above it, into which each wave can 
penetrate. If we creep to the very edge of the stack, where 
it goes down sheer into the sea, we shall learn further as to 
the irregularities in its wall. 

On one hand the stack sends out a promontory, and we 
can see the side-face of this, with the strata running across 
it like sloping bands. Under some of the ledges formed by 
them, long hollows and caves occur, roofed by the bed above ; 
and pebbles and boulders lie in these depressions. As each 
wave breaks, these caves are flooded, and the stones are flung 
inward against the farther wall. A swirling movement again 



94 OPEN-AIR STUDIES 

takes place as the water retreats, and each time destructive 
work is done. The sea, with its tremendous battering-power, 
is excavating caves, just as the streams make pot-holes ; only 
the action is horizontal, rather than vertical, the water lashing 
like a whip around the flanks of the sea-stacks and islets. 

The cleft near us is only a widened joint, several of which 
run across the mass ; and the form of the whole stack is 
largely influenced by them. The constant attack of the spray 
helps the rock to decompose ; films of crumbling alteration- 
products are formed on the surfaces of the joints ; and blocks 
become finally unsteady and fall into the widening gully. 
Down below, the sea uses much more effective means ; the 
fallen masses, as well as the pebbles swept in from other 
sources, are laid hold of as battering-tools and are hurled 
against the rock ; and thus a cave is formed, wide and shallow 
at first, but continually deepening, its roof often falling in 
and producing a very marked ravine in the sea-stack. Our 
cleft has doubtless become wider by the removal in this way 
of supporting masses from its base. 

Out beyond us, quite surrounded by the incoming water, 
is a stack which is bored through completely by an arch, as 
bold in its proportions as that of a cathedral-transept. The 
cave-cutting action has here drilled the mass through to the 
other side, and it is only a question as to when the roof will 
be so far weakened as to fall. In that case one pillar of the 
arch will form a new stack or sea-pinnacle, which will become 
all the more isolated from the main mass as the sea swirls 
freely round it. 

This is the history of the tiny islands round about each 
of the main stacks ; over many of them the sea now flows 
freely at high tide, and as many more must be permanently 
below its surface. Every fall of rock furnishes the dashing 
breakers with fresh and unworn tools ; every grinding of one 
mass on another supplies sand and grit, which smooth the 
surfaces and enable the water to slip on uninterruptedly to 
further conquests. 

As we look out towards the lighthouse upon the most 
distant isle, we realise that the dangerous reach between it 
and ourselves is filled with the worn-down stumps of islets 
and the wreck of huge stacks of former days. All this 
region was once part of the solid land behind us ; the islets 
were once united as a great promontory stretching a mile to 



ALONG THE SHORE 95 

seaward ; and the waves have worked their will with it, 
cutting it up into squares, like a regiment overwhelmed by 
cavalry, and then attacking the bluffs separately until the 
whole will in time inevitably disappear. When our eye has 
got used to them, we can detect the beginnings of caves and 
natural arches in every exposed face round us ; and beneath 
us we have the voice of the invader, triumphing in the dark- 
ness of the clefts. 

The spray now rises too near us, and is flung by the 
wind across the seaward face. We must descend to the 
little sand-spit, which still finds shelter behind the stack. 
There is very little of it, and the pebbles stuck into it are 
mostly derived from the stack itself. Soon the sea will lap 
round and cover it, and will some day shatter its protector 
and sweep the spot clean and clear, down to the more re- 
sisting ribs of rock below. 

These ribs of rock now represent for us the ruins of 
the older headland. When we have crossed them again, 
among the barnacles and seaweeds, to the foot of the great 
cliff, we can look back and watch the sea racing in over 
them, wave upon wave, and rattling the pebbles across their 
upturned and worn-down edges. Here and there a big 
stone lies, resting on two adjacent ribs, and ready to be 
moved, in days of serious storm, as a formidable assailant 
of the rocks. As the tide comes in across this shelving sur- 
face, we see how the waves lose their force ; but they still 
have strength to burst upon the great rock-wall, when the 
water rises to its fulness. If, as we saw among the stacks 
and islets, the bulwarks of the shore are being cut away, the 
sea will be able to stretch farther and farther inland, instead 
of merely spreading over the debris to a line along which it 
is at last powerless to act. 

In fact, a gently sloping surface is being formed by the 
action of this great horizontal saw — an old familiar com- 
parison which cannot easily be bettered. And the dragging 
of the loose blocks and sand over this surface is continually 
wearing it down upon the seaward side, and enabling the 
inner edge to encroach slowly upon the land. 

Such a surface was called by Sir Andrew Ramsay a 

plain of mairine denudation ; the title is a long one, but 

is far more expressive than the attempts made in some 
sciences to cover up each conception in a single word of 



96 OPEN-AIR STUDIES 

Greek. When we view from some distance the sea rolling 
in across such a plain, especially when the great green waves 
are driven by a stiff gale upon the coast, we may indeed 
wonder how many bars of rock survive at all above the 
surface (Plate IV). 

We look round at the curve of the bay itself, and we 
see that the water is now high upon the beach of sand. 
Over against the village it is beating on the little promon- 
tory, and filling the harbour, foaming against the piers. At 
spring-tides, and in stormy weather, we know how the waves 
extend right up to the low cliflE that runs all round the bay ; 
aud we can realise now that this curving indentation, a mile 
across, is also a product of sea-action. The bay itself is only 
an extended form of the hollows cut in the face of the sea- 
stacks. 

The general tendency of the sea's attack is to excavate 
wide sweeping inlets. It cannot go on indefinitely surging 
up a narrow channel ; the mouth becomes cut away on each 
side and widened, and the broad flow of the waters forms a 
semicircular bay. 

Some of the most interesting examples of this action 
are to be seen in the ^' coves" of Dorset. A bed of hard 
limestone forms in places, such as Lulworth, the bulwark of 
the land ; and behind it are other limestones, sands, and 
clays, and then the soft massive limestone known as chalk. 
The battering of the sea makes holes and channels through 
the barrier ; and then the water, meeting with weaker 
materials, carves out bays behind it. It will be long before 
the more resisting barrier of Portland stone is worn away, 
so as to leave these "coves" properly open to the sea. 
When this happens, several smaller ones will probably unite 
quickly, and will form one broad sweeping bay. 

The loss of land before the sea is often so rapid as dis- 
tinctly to aflfect the towns and farms along the coast. The 
military road and the footpaths along the south cliffs of the 
Isle of Wight are always liable to disturbance, and the 
difficulties are much increased by the rapid cutting back due 
to fresh-water streams as they fall over the soft sandstone 
wall. At Cromer, in Norfolk, where the loose pebbly cliffs 
lend themselves so well to the formation of model deltas, 
the sea rapidly undercuts the material and causes the coast- 
line to recede some six feet annually. Churches of known 



ALONG THE SHORE 97 

date have often served as a means of measuring the amount 
of marine denudation in the course of several centuries; 
and many on our eastern English coasts have gone over 
altogether into the sea.^ 

Mr. Henry G. Spearing '^ has observed that on the exposed 
face of Bideford Bay, where Westward Ho stands, the sea 
has recently removed the land at the rate of about thirty feet 
a year. The coast in this case is of course formed of soft 
materials, and a new cliflE twelve feet high has been cut at 
one point in the clays. 

Similar " invasions " of the sea, so rapid as to seem like 
floods to the bewildered and unobservant inhabitants, have 
cut away the sandy south-east coast of Kent between the 
Soman period and our own, depriving us of a strip of land 
nearly four miles wide. The story of the loss of Earl Godwin's 
estates is probably a true one, and the Goodwin Sands to 
this day are dangerous banks upon the site of the eleventh 
century shore-line. The recent disastrous slips at Sandgate ^ 
show how the action of springs among permeable strata 
conspire with the sea to bring about the destruction of the 
land. 

It is a somewhat melancholy reflection that the scour of 
the waters in the English Channel is widening the Straits of 
Dover on both the French and English sides, and this at the 
rate of about a yard per annum. Belfast Lough is also 
growing, as is shown by the approach of the three-fathom 
line, marked on successive charts, to the coast-towns upon 
either side.* But the artificial protections set up along the 
sea-face of most of our coast-towns do much to preserve the 
cliffs behind. 

The huge black cliff under which we are still standing 
towers vertically for some 700 feet ; and a number of causes 
work together to maintain this magnificent sea-front. The 
rock is massive, and has strongly developed vertical joints ; 
frost, in our climate, occasionally splits off the upper blocks, 
as it does among the cirques of the mountains ; and the sea 
is sufficiently powerful to break up and remove the fallen 

^ See H. B. Woodward, " Geology of England and Wales,'* 2nd edition, 

P* 594» &C' • 

^ QuaH. Journ. Oeol, Soc^ vol. xl (1884), p. 474. 

' See Nature^ vol. xlvii (1893), pp. 449 and 467. 

* Miss M. K, Andrews, Irish Naturalist , 1893, p, 47. 

G 



98 OPEN-AIR STUDIES 

masses, so that they afford no real protection to the base. 
The waves are always undermining the huge wall, and bring- 
ing down vast slides of rock along the joint-planes ; the 
talus-blocks are gradually broken up, and become worn down 
into mere pebbles, which serve to scour out and deepen the 
sea-caves. On looking up the face of the cliff, it is not 
difficult to see whence the recent falls have come, by the 
fresher nature of the scars that they have produced. And a 
still more striking spectacle awaits us if we ascend to the 
summit by way of the gentle grass-slopes in the rear. 

The beach is now nearly covered with the water, and we 
can leave it until a more favourable occasion. When we reach 
the higher ground, we can see, as in a map, the distant 
headlands jutting out, north and south of us, with curving 
bays between them. All along the coast we have evidence 
of the aggressive nature of the sea ; and the forms of these 
promontories and indentations, which at first seemed de- 
signed for our affliction during our early studies in the 
school-atlas, now begin to have a new meaning ; we find 
that every sea-cove has an interesting lesson of its own. 

Here, among the tufts of grass and heather, we must 
walk carefully towards the edge of the great cliff. As we 
do so, we cross several deep gullies, running roughly parallel 
with the sea-face. A little observation shows us that we 
are here present at the birth of mighty landslips ; and the 
ground is already prepared to give way beneath our feet. 
The enormous rock-mass is fissured by its joints, and the 
removal of material from its front and base causes flakes, as 
it were, consisting of thousands of tons of material, to slip 
outwards and ultimately to fall. Thus the cliff-face may 
recede suddenly at certain points by several feet in a few 
seconds ; the nobler the scale upon which it is developed, 
the more liable it is, like a lofty mountain, to catastrophes 
and sudden denudation. 

Thus it is by no means only the softer strata that suffer 
rapidly from the battery of the sea. The sandstone isle of 
Heligoland^ is thus a mere fraction of its former size, as 
recorded in historical documents, perhaps only a quarter 
being now left; and a neighbouring island, the cliffs of 
which were nearly 200 feet high in the seventeenth century, 

^ Reclus, "LaTerre," 3me ddit., tome ii, p. 192. 



ALONG THE SHORE 99 

has practically disappeared, leaving only long ridges of blown 
sand. Now that accurate maps have been constructed, 
showing the coast-lines of most countries, it is surpris- 
ing to note what changes occur in a hundred or even fifty 
years. 

Our great headland may have formerly been part of a 
hill situated far inland ; the present grass-slope falls towards 
the land, showing that more than half the mass has been cut 
away. The highest point is, in fact, along the very summit 
of the cliff. Farther down the coast we can see a hill, the 
base of which is just being attacked ; a low cliff has been 
carved out of it, and the ground rises from the edge of this 
to the summit of the hill, a mile or so inward from the sea. 
Again, on leaving Newhaven, in Sussex, by the steamer for 
Dieppe, a number of grassy combes are seen breaking the 
line of the chalk cliffs, and terminating half-way up them 
above the sea. These represent old valleys which once ran 
down to near the sea-level ; but the white cliff has been 
formed across them, leaving only their higher regions facing 
us ; and in time these evidences of the old form of the land- 
surface will no doubt entirely disappear. 

So some cliffs grow higher as the sea causes the coast- 
line to recede ; others, like our great one, will become less 
and less important. As the sea advances, it will meet with 
various irregularities that have been already carved out by 
rain and rivers on the land- surface ; and the form of the 
coast may thus change quite abruptly, while the flow of the 
tides and of the permanent currents may be interfered with 
in a striking manner, through the sea having to accommodate 
itself to indentations for which it is not at all responsible. 

So far we have regarded only the denuding action of the 
sea. Enormous quantities of material are annually removed 
from the coast in certain regions ; and M. Marchal has given 
us the figure of 10,000,000 cubic metres ^ as the amount taken 
each year by the English Channel in the neighbourhood of 
Kent and Normandy. That is equivalent to a bank of rock 
a mile long, 300 feet in width, and about 223 feet in height. 
Now, all this material must go somewhere; for only a small 
portion disappears in solution in the sea. The same agent 
that destroys so persistently in one place may, like a river, 

^ Reclus, **La Terre," 3me ddit., tome ii, p. 175. 



■^ 



lOO OPEN-AIR STUDIES 

transport the debris to another area, and there peaceably 
construct new land. 

As a matter of fact, many of the pebbles formed by frio 
tion from blocks that have fallen into the sea, and part of the 
finer sand thus produced, are continually travelling along the 
coast. Much of the material no doubt runs down the steeper 
seaward face that bounds the plain of marine denudation ; 
here it finally escapes from the action of the waves, and is 
only slightly affiected by the pennanent currents of the sea. 
It thus forms a broad submarine talus, a shoal which covers 
up the old surface of erosion, and which stretches some way 
towards the true oceanic floor. At its upper edge the material 
is worked on by the breakers as it slides outwards from the 
coast, and the finest substances, the tiny particles of clay, 
become sifted out from the sand-grains and are washed away 
to far greater distances. The sand is, moreover, in part 
separated from the pebbles and from the small unrolled rock- 
fragments, and is removed to an intermediate distance. Thus 
the dUhris of the cliffs undergoes a steady selective process, 
like the materials at a river-mouth. We have pebble-banks 
formed typically near the shore ; then sand-banks farther out 
to sea ; and deposits of fine mud beyond these, the last named 
occurring even at depths of between looo and 2000 fathoms. 
The mud will consolidate as stiff clay, or, if it preserves a 
sti*atification and splits into fine layers, it will form the rock 
known as shale. 

Local formations on the coast will interfere with the re- 
gularity of such deposits. Thus, near the mouth of a muddy 
river, clay-banks will accumulate close to the shore itself ; 
there is too great a supply for the sea to carry off. Enor- 
mous sand-banks, again, devoid of coarser fragments, may be 
formed close under soft sandstone cliffs ; for this rock breaks 
up so readily that no true pebble-beach can arise. As usual, 
each locality will give us some special features of its own, and 
will provide interesting modifications of the general plan of 
shore-deposits. 

A mingling of one deposit with another on the same 
horizon must always occur, due to the imperfect sifting. 
Thus pebble-beaches graduate into pebbly sands, and sands 
into sandy clays, known as Loams. 

Clays, again, often contain a large proportion of calcium 
carbonate, due to the shells included in them. When the 



ALONG THE SHORE / . lOI 

proportion amounts to one-third of the total weight or more, 
the clay becomes almost a clayey limestone, and ipay be called 

a MarU '/*•", 

We can, fortunately, study these formations in maoy*places 
between high and low water-marks. There are regiops'^Jiere 
the sea confines itself to laying down new material j'Vibere 
the scour of the currents only serves to bring substancftX in 
suspension from other places which are being denuded f^and 
here, then, the land grows by a process opposite to that of .*• 
the formation of a delta. The additions to the coast are, id 
fact, the deltas of oceanic streams ; the carrying power oh\.-\ 
these currents is reduced when they strike upon projecting -•" 
land. 

For such deposition a quiet area is indispensable ; a ridge 
exposed to storms will be despoiled of any material that may 
have been laid down upon it in quieter times, just as a valley 
may be kept clear by recurrent flood-periods in its torrent. 
The shifting form of estuarine banks, and of other products 
of denudation along a coast, may easily cause a bay to receive 
deposits during one series of years, and may then allow it to 
be swept clear again during another series. 

In the hollow of our own little bay, beginning in the 
shelter of the great rock-headland, and running round 
towards the harbour, we find an area in which marine denu- 
dation is at present at an end. The cliff once cut out is 
becoming covered with soil-slips, and is in places grass- 
grown ; and its form is already so much altered that a wind- 
ing cart-track has been made across the face of it, by which 
rough vehicles are led down for the gathering of seaweed on 
the shore. At its foot are banks of pebbles, untouched by 
the water except during those storms that happen to coincide 
with the highest tides of the month. Beyond them stretches 
a gently sloping and pebbly beach, the stones becoming 
gradually fewer and fewer as we go seaward, until we come 
to the zone selected by the bathers, where all is fine and 
shelly sand. We must come down as the tide is going out, 
and view this second, this accumulative aspect of the sea. 

The highest ridges of the beach, forming terraces under 
the old cliff, result from the transporting power of the waves 

^ This is the true sense of the word *' Marl," as adopted from agriculturists, 
though the term is often much misused. See J. MaccuUoch, ** A Geological 
Classification of Rocks " (1821), p. 630. 






* • 

* • 






1 02 . •.. . OPEN-AIR STUDIES 

• 

daring exceptional storms. The dash of the water nnder 
these cirejamstances carries out any sand again, bnt leaves 
the peJ5bfe*i^ hurled up one upon the other. They lie there 
with thc'ir flatter surfaces fairly horizontal ; but, apart from 
this,*ffere is little appearance of stratification. In one place 
a fi^5p,'(5f peaty soil from the top of the old cliff has spread out 
afKl, 'formed a layer, containing rootlets and a few potato- 
stalks, on the surface of the pebbly terrace; and fresh 
'•..pebbles have already been flung on to the top of it, so 
.. tfiat it is likely to form a distinct stratum in the beach. 
•'V^i'When finally consolidated, we should call the pebble-beds 
'•* conglomerates; and the black earthy layer in between 
them would be said to be lignitic, or full of woody vegetable 
remains. Any stems of trees or pieces of broken fencing 
that have been brought down with it would become con- 
verted into a deep brown or black substance known as 
lignite. The gaseous products of their decomposition pass 
slowly off, the combinations of oxygen, hydrogen, and nitro- 
gen being more freely formed than those of the carbon ; 
hence the latter constituent rises in proportion in the 
residue, and forms more than 60 per cent, of lignite. 

Flaky shells, easily lifted by the waves, are found here 
cast up with the pebbles and entombed among them. Oyster- 
shells thus often predominate ; but we must be careful to 
avoid places where the fishing-people have thrown out their 
rubbisli-heaps, for quantities of molluscan shells are sure to 
occur in these, and may have been brought artificially from 
some distance. But an examination of the pebbles them- 
selves will give us a good idea of the work of the sea as a 
common carrier. 

A layer of corks may occur on the surface of the beach ; 
these accumulate in the areas of deposition from the daily 
passenger -steamers that go up and down the Channel. 
Cinders from the furnaces are also frequent ; and these two 
sets of obj(^cts remind us how anything which floats without 
easily becoming waterlogged may be carried indefinitely 
about the world upon the surface-currents of the ocean. 
Seeds of strange plants have thus been conveyed from one 
country to another, and have occasionally found suitable^ 
soil, and have added permanently to the vegetation of their 
^fe^ new home. Man himself has often been similarly distributed, 
^^^ much against his will, being carried in canoes before the 



ALONG THE SHORE 103 

great continuous winds, and landed, perhaps, on an unknown 
shore to form the first population of a continent. These 
ugly little banks of corks are thus not to be despised ; ob- 
servations of such trivial objects may help us to determine 
the direction of the great ocean-streams. 

But the pebbles are more distinctly interesting. Elderly 
ladies and gentlemen who come down here as summer- 
visitors spend hours in collecting them, on account of their 
very variety and beauty. A great number of them come 
from the waste of the sea-stacks and the grim dark headland 
yonder ; they are already admirably worn and rounded, and 
we see how the daily friction smooths and grinds down even 
the hardest rocks. But here is a bright red pebble, a jasper, 
unlike anything in the solid walls of our own bay ; and all 
around are others made of hard altered sandstone, called 
"quartzite," the nearest mass of which lies some twenty 
miles away to the south. Here, again, is a green and black 
pebble which we cannot easily identify ; but our mineralogical 
friends may make a microscopic section of it, and may tell 
us that it is from a unique mass occurring on the coast of 
Norway. Such a specimen has probably been brought here 
on a block of floating ice, in days when these seas were 
colder or when currents ran in other directions than at 
present. Trees that have fallen into the sea may also bring 
foreign stones entangled in their roots ; and many seaweeds 
cling to stones on the sea-bottom, and, when torn up by 
storms, carry these specimens about with them to long 
distances. 

It is not a matter that must be dealt with lightly, this 
tracing of the place of origin of pebbles gathered on a 
beach ; and we must remember that they may have come 
from some outlying and even adjacent point which has been 
worn entirely away. The nuggets of gold in the rivers of 
South America, and, it is said, the famous diamonds of 
Golconda, serve to illustrate this point. They occurred 
freely in the alluvial deposits of the rivers ; but a search for 
them in the rocks up the valleys has proved disappointing, 
their original matrix having been denuded off the face of 
the earth. 

But, in the case of the pebbles of quartzite on our beach, 
the evidence is pretty clear, and a walk south along the 
coast confirms our first supposition. The pebbles are re- 




I04 OPEN-AIR STUDIES 

placed by huge boulders as we reach the actual promontory 
of quartzite, and the sea is evidently still maintaining the 
supply. All along the intervening coast, in every sheltered 
inlet, pebbles from this same source can be found; and 
clearly they are still being swept round our great headland 
into the quieter waters of the bay. 

Some of the pebbles on our beach are thrown up from 
the estuarine deposits, and were already rounded by the 
stream before they came into the sea. Just as when torrents 
empty themselves into lakes, so beds of marine conglomerate 
often arise, in which the only part played by the wider 
waters is the smoothing out and spreading of material which 
has been already rounded. 

In conglomerates very few shells are found, because, in 
the first place, the molluscs cannot live amid the pounding 
action of the pebbles; and because, in the second place, 
any dead shells that are washed in become speedily reduced 
to powder. But farther down the beach, where the finer 
sand stretches, abundant shells may be discovered, together 
with dead crabs and other shore-animals, which become 
buried as the mass accumulates. The smoothing and strati- 
fying action of the sea is apparent in the even surface of 
these sands ; every tide, the wash forward and backward of 
every wave that breaks, tends towards a spreading and a 
distribution of the material, and uniform strata are thus 
deposited over wide areas of the coast. Between the tides, 
we may note how the water has here and there raised the 
sand into ribs and delicate ridges, ripple-marks as they are 
called, the particles of sand being pushed forward in one 
direction like a wave, and then dropped where the water 
could no longer sustain them. The sea-salt may dry on the 
surface of these when they become exposed, and will tend 
to make the structure firmer. The sun also, drying the 
material, causes cracks to open in the sand or mud of the 
beach; while the ebbing tide, running out round little 
stones, forms grooves and tiny channels in the deposit. 
Man, moreover, and other animals leave footprints and 
tracks as they pass over the yielding surface. 

Current-bedding, like that of river-deposits, must clearly 
occur in places, especially where changing sand-banks alter 
the directions of local currents from year to year ; but marine 
deposits as a whole are more regular than those produced by 



ALONG THE SHORE I OS 

any action on the land, especially where the material is 
spread out at some distance from the coast. A change in 
the direction of the transporting currents, in the material 
supplied by local rivers, or the fact that the sea has begun 
to attack some rock hitherto beyond its reach — any of these 
occurrences may cause the deposition of a new stratum of 
different mineral character to that preceding it. 

Sea-sand is so familiar, ever since, as children, we dug in 
it with wooden spades, that the variety of its constituents is 
hardly suspected by us. But it is well worth while to fill a 
box with the material and to bring it home for examination. 

The best instrument to aid in this examination is a sieve. 
K special ones are not to hand, sieves may be made by knock- 
ing the bottoms out of wooden boxes about 6 inches square, 
and fastening muslin of various degrees of fineness on to the 
sides instead. But it is very useful to have a set of 6-inch 
circular chemical sieves, costing altogether about 8s. 6d. 
Three sieves of brass-wire, with meshes containing respec- 
tively 30, 60, and 90 holes to the linear inch, are fixed in tin 
cases, and are so made that they will fit into one another, 
leaving spaces some 2J inches deep between. The coarsest 
sieve lies at the top, and a cover fits upon it ; beneath the 
finest, again, a tin dish fits exactly, to catch whatever particles 
get through the 90-hole mesh. The whole set now forms a 
cylindrical box, crossed at regular intervals by the three wire 
nets. If it is necessary to sift even the fine dust that has 
escaped into the lowest dish, an extra sieve can be made of 
very fine silk, and the finest particles of all can be washed 
through this under a water-tap. 

Let us take a handful of our sand and leave it over-night 
in a basin of water, to cleanse it from the sea-salt that has 
been deposited upon it. We must now dry it thoroughly — 
an oven will do for this — until the particles no longer stick 
to one another. Then we pour it upon the uppermost sieve, 
put on the cover, and shake the whole set of sieves from side 
to side, with the addition of a circular motion. 

In two minutes or so a complete sifting will have taken 
place, according to the coarseness of the materials. Let us 
separate the sieves from one another, and pour out their 
contents into little card-trays, putting a number in the 
bottom of each to distinguish them from one another. The 
top sieve contains all the constituents that are more than 




I06 OPEN-AIR STUDIES 

one-thirtieth of an inch in diameter. Here are little stones, 
which are the smaller pebbles of the beach, and flakes of 
broken seaweed, and fair-sized fragments of shells, and a few 
perfect shells, the small size of which has enabled them to 
escape destruction. One or two delicate glassy-looking rods 
are the spines of sea-urchins, and are seen, when examined 
under a low power of any common microscope, to be orna- 
mented all over with ribs and little projections. Probably 
the second sieve contains a larger quantity of material, and 
here we find much the same constituents as in No. i, only 
they are of smaller size. The most interesting objects are 
the minute coiled glassy-looking shells, almost all perfect, 
which can be well seen under a microscope magnifying about 
25 diameters. They are perforated by minute holes, and 
consist of numerous chambers, like the well-known shell of 
the pearly Nautilus. These are the shells of Foraminifera, 
some of the humblest animals on the globe, the jelly-like 
bodies of which are capable of forming these complex struc- 
tures out of calcium carbonate, the materials being derived 
from those in solution in sea- water. Other dull white and 
practically opaque foraminifera are likely to be seen, and can 
be identified and named by comparison with the figures in 
special works upon the subject.^ 

The minerals derived from the friction of the various 
pebbles are found fairly separated from one another in this 
sifting ; that is to say, few entire pebbles have come through, 
the particles allowed to pass being so small that each consists 
typically of one mineral alone. In sifting No. 3, where the 
grains are between one-sixtieth and one-ninetieth of an inch 
in diameter, most marine sands will yield a material con- 
sisting of very well-divided mineral particles. 

Scarcely any shell-fragments now remain, and quartz is 
clearly the predominant substance. Its hard grains, with 
vitreous lustre and irregularly curved surfaces of fracture, 
gleam like little lumps of glass under the microscope. Black 
minerals are probably also present, and some can be lifted 
out with a magnet, showing the presence of magnetite. The 
others may be hornblende, augite, tourmaline, &c. Tiny 
flakes of mica may also be seen, some silvery, some a rich 
bronze-black. If we wish to extract any particular grain 
from the heap as seen under the lens, the point of a fine 

' See H. B. Brady, " Report on the Foraminifera," Challenger Reports^ 1884. 



ALONG THE SHORE IO7 

colour-brush or of a sharpened rod of wood, just moistened, 
will serve to secure it, and it can then be lifted out and 
dropped off into water upon a slip of glass or in a watch- 
glass for chemical or other treatment (see p. 23). 

The dust in the bottom pan will probably be too fine for 
convenient study ; but the vast bulk of it can be seen to con- 
sist of quartz. As sieve No. 3 and this pan contain almost all 
the sand put into the uppermost sieve, it is clear that, when 
the shells are deducted, the chief constituent of our sea-sand 
is simply quartz. The grains, being so small, are very little 
rounded, and their practically indestructible character makes 
them survive most of the other minerals that may have 
originally been mingled with them. Doubtless any clay 
particles have been sifted out long ago by the action of the 
waves, such bodies being sometimes so minute that 17,000 of 
them might be arranged along a single inch. A sand left to 
itself in the shallower portions of the sea, without the addition 
of new shells or of matter from the land, would tend to become 
more and more purely a bank of colourless quartz-grains. 

Sometimes a foraminiferal shell is found which is filled 
with a soft green earthy substance, easily crushed between 
two glass plates or under the blade of a knife. This is 
Olauconitey a hydrous silicate of aluminium, iron (in the 
condition of peroxide), potassium, magnesium, and calcium.^ 
Its precise mode of origin is obscure ; but Messrs. Murray 
and Renard, in the report quoted, believe that it arises 
partly by chemical changes, which go on between the dead 
organic matter within the shell and the fine mud that has 
oozed into the chambers, and partly by absorption of sub- 
stances, such as potash, from the sea-water. The glauconite 
in any case grows until it completely fills the shell and 
even bursts it;^ and, if the shell breaks away or becomes 
dissolved, the material is set free as a green grain which is 
a cast of the interior of the foraminifer. 

We shall find these grains thrown up only sparingly on 
our coasts ; but they are formed abundantly at a little 
distance from the shore, and mostly at a depth of about 
100 fathoms. In many old sandstones and limestones they 
form a great part of the rock, giving us Greensands and 
Glauconitic limestones, and showing that the same complex 

^ For recent analyses, see " Report on the Deep-Sea Deposits," CliaUenffer 
Heports, 189T, p. 387. ^ Ibid., Plate xxv. 




I08 OPEN-AIR STUDIES 

chemical processes went on, as now, when those materials 
were being deposited. 

It is obvious that in our walk along the shore we are 
only on the threshold of all the wonders of the deep. The 
deposits of soft separated mud, for instance, will be found 
in their purity farther out; they form the bottom of the 
deeper portions of all land-locked seas, but rarely extend in 
the great oceans to 500 miles from the coast. The materials 
carried in suspension by the sea as products of denuda- 
tion of the land are, indeed, mostly deposited as a fringe 
some 1 50 to 200 miles wide round the continents, forming 
thick banks along the coast itself, and becoming thinner 
and thinner down the slope to seaward. Only bodies that 
can float, such as volcanic ash and lumps of pumice, which 
are full of cavities, find their way far enough from shore to 
sail over the real oceanic depths. Here they may become 
decomposed and waterlogged, and may thus sink, to be 
deposited in the uttermost parts of the sea. As a rule, 
the only deposits found by dredging operations after 2500 
fathoms (15,000 feet) are due to animal and vegetable life 
or to this decomposed volcanic material. Thus the sea- 
bottom at one of the greatest depths ever accurately 
sounded was found to be covered with the skeletons of 
organisms that take silica from the sea — Radiolarians, 
certain Sponges, and the humble plants called Diatoms. 
The depth was 4475 fathoms (26,850 feet), and the sound- 
ing was made east of the Philippine Islands, and about 
one-third of the distance between New Guinea and Japan. ^ 
The mineral particles in this deposit were derived entirely 
from volcanic rocks, or from meteorites coming from outside 
our own planet. 

We must not venture away to sea into these fascinating 
regions ; but we may enquire where it is that the shell-fish, 
whose remains we see cast up so often, find their most 
agreeable dwelling-place. They may live close in to the 
coast, if no rivers are discharging debris upon them. They 
choose the purest waters, consistently with the presence of 
a constant food-supply; and all the familiar genera live 
at depths less than fifty fathoms. Where conditions are 
favourable, their shells accumulate, as the animals die, in 
vast banks, sometimes formed principally of one particular 

^ *' Report on Deep-Sea Deposits," Challenger Reports^ p. 204. 



ALONG THE SHORE IO9 

species. The constitution of the shells is calcium carbonate, 
either in the form of calcite or aragonite ; and hence beds 
of Limestone are being formed to-day by the accumulation 
of shells beneath the level of the sea. 

Calcium carbonate being soluble in water containing 
carbon dioxide, it is not surprising that the sea itself, with 
its included gases, attacks great heaps of dead shells, and 
removes their surface-layers, or even dissolves them alto- 
gether. The carbon dioxide is in great part derived from 
the decay of animal matter in the sea, and its solvent power 
is increased at great depths by the pressure of the over- 
lying layers of water. Meanwhile, the currents are always 
washing the shell-bank out at its edges, and rubbing the 
remains together, producing a fine limestone-rmtd. The 
water, charged freshly with calcium carbonate in solution, 
wanders through the mass, and helps to cement many of 
the fragments together, a re-deposition of the dissolved 
material taking place. Calcium carbonate is also deposited 
when fresh water strongly charged with it comes in contact 
with saline waters.^ The chemical reactions that take place 
are not yet clearly known ; but it is certain that stones and 
shells may become cemented in our harbours by dense deposits 
of chemically formed limestone. 

The limestone-mud and the tiny foraminiferal shells also 
get washed inside the larger shells and completely fill them ; 
and thus the foundations of a solid bed of limestone are 
laid down. This bed, like the sand-banks and mud-banks, 
will be thinner at its edges, ultimately dying out all round, 
and will be thicker in the centre, below the point where the 
living molluscs are most thriving. Stratified beds of lime- 
stone, the shell-banks of bygone ages, are found to have this 
structure when examined in quarry-sections, their form being 
that of a greatly flattened plano-convex or double-convex lens, 
several such banks lying on or dovetailing into one another. 

Sometimes a flow of mud or sand will be brought across 
the shell-bank, and will check its further growth ; the bank 
may be temporarily killed. Then it again begins to grow, 
the materials now piled on the original bed helping to 
flatten it down and to give it regularity as a limestone 

^ See J. Murray and R. Irvine, ** Coral-Reefs and other Carbonate of 
Lime Formations in Modem Seas," Nature, vol. xlii (1890), p. 165 ; and 
Jukes-Browne, " Handbook of Physical Geology," 2nd edit., p. 274. 



I I O OPEN-AIR STUDIES 

stratum. Thus alternations of limestone with other rocks 
may occur at some points, and continuous beds of limestone, 
stratified by sea-action, at others. 

In some climates coral-animals^ form, by their closely 
grown or branching skeletons, limestone coral-reefs of great 
extent. Certain seaweeds that strengthen themselves with 
calcium carbonate also contribute largely to these massive 
structures. Lumps of dead coral, broken off by the surf, are 
washed down the slopes and spread the reef steadily seaward ; 
and on its edge all manner of moUuscan shells become mingled 
with wave-rolled fragments of coral and of calcareous sea- 
weeds. The reef becomes thus a stratified limestone on its 
outer margin ; and even within it the swaying action of the 
surf lays out limestone-mud between the branching skeletons 
of the coral, and thus produces a kind of stratification.^ 
Cementing of the whole mass soon goes on, and the calcium 
carbonate dissolved off one part of the reef becomes deposited 
as a means of consolidating the loose blocks at another. Here, 
then, we have an example, from warmer climes, of how lime- 
stone may accumulate with considerable rapidity near a shore. 

A pleasing instance of the re-deposition of calcium car- 
bonate from solution in sea-water is seen in the formation of 
oolitic grains upon the flanks of coral-reefs in the West 
Indies. Little rolling bodies, such as grains of sand or 
shell-fragments, become surrounded by successive coats of 
aragonite ; and spheroidal grains result, perhaps a millimetre 
or two in diameter, which accumulate to form " oolitic lime- 
stones *' or "oolites," becoming subsequently cemented to- 
gether by calcite into a firm mass. It has been stated that 
in some cases, at any rate, minute algae aid in the formation 
of oolitic grains, as they do in that of limestones deposited 
from hot springs. 

The humble foraminifera also form beds of limestone, 
which spread evenly, and free from foreign matter, over great 
areas of the ocean. The remains of those species that live 
near the shore become, as we have seen, mingled with the 
ordinary sea-sand, and their abundance is therefore liable to 
be masked. But some of the most important foraminifera 

* The term *' coral-insect " should never be used, the animal being a polype 
of far lower organisation than an insect. 

- Von Richthofen, *'Ueber Mendola - Dolomit und Schlem-Dolomit," 
Zeitschrifl d, dcutach, geol. GeselL, Bd. xxvi (1874 ), p. 225. 



ALONG THE SHORE I I I 

swim upon the surface of the water, and consequently flourish 
above any ocean-depth ; hence limestones may be formed of 
their remains alone, out beyond the zone of materials brought 
in suspension from the land. The famous genus Globigerina 
thus furnishes a white deposit or " ooze " over the ocean-floor 
at depths of about 2000 fathoms, such deposits being mingled 
with sand-grains and clay -particles as we approach 500 
fathoms. At depths of about 3000 fathoms and more, only 
red clays, derived from* waterlogged pumice and from the 
ash of submarine eruptions, together with remains of those 
organisms that make their skeletons of silica, are found over 
the ocean-floor. The molluscs known as pteropods, and the 
great bulk of the foraminifera, swim freely above these abys- 
mal depths ; but the sea-water dissolves away the dead shells 
during their long descent, and the number of fathoms from 
which a sample of marine deposits has been procured will give 
a fair idea of the proportion of calcium carbonate that it has 
retained. 

Shells, then, and the skeletons of marine organisms, may 
accumulate to form limestone rocks, while here and there 
beds of siliceous remains give us deposits of a flinty character. 
The most extensive examples of the latter are the ZHatom- 
oozes, formed by the humble plants already referred to, which 
lie in a zone round the laud-deposits of the Antarctic conti- 
nent.^ But the rate at which organic agents form rock 
masses is slow indeed when compared to the rapidity with 
which inorganic agents, such as currents, may bring together 
materials in suspension. New land may be built up visibly 
by the sea, just as surely as old land may at other points be 
destroyed. Usually the growth of land is connected with the 
action of rivers also, and is most noticeable in the neighbour- 
hood of some important delta ; but the deposits are sifted aud 
arranged in their new positions by the sea, and marine shells 
become embedded in them. As an instance of this, M. Eeclus ^ 
calls attention to the remarkable increase of Cape Ferret, in 
the Department of the Gironde, under the joint action of wind 
and river and sea-tides. From 1768 to 1826 the headland 
grew 5 kilometres (three miles or so) towards the south, the 

^ See the interesting Chart I, " Deep-Sea Deposits," Challenger Reports. 
It must be remembered that the area occupied by the Diatom-ooze is greatly 
exaggerated, owing to the map being on Mercator*B projection. 

^ " La Terre," 3me ddit., tome ii, p. 215. 



I 1 2 OPEN-AIR STUDIES 

rate being 20 to 25 centimetres a day. Since then, however, 
it has been in part destroyed by the sea and reconstructed. 

One of the best examples of new land formed on the 
British coasts is the broad promontory of Dunge Ness in the 
east of Kent and Sussex. It is curious to ascend the ridge 
that stretches between Aldington and Hythe, and to look 
down into the level land of corn below, and to realise that 
we are standing on a sea-cliff of comparatively recent times. 
Dunge Ness itself is formed of marine pebbles of flint carried 
from the west ; the shingle is still so loose that no roads can 
be maintained across it, and the inhabitants of the surround- 
ing villages traverse it on peculiar flat wooden shoes.^ 

The point of the Ness has grown for two hundred years 
at the rate of 36 feet (11 metres) a year, or 3 cm. a day. The 
sea seems anciently to have extended up to Newenden, some 
eight miles from the present coast, and the river-deltas en- 
croached later on the old marine deposits. The Eomans had 
a harbour at Portus Lemanis, the present Lympne, and took 
ship under the cliff which is now one and a half miles inland. 
To take another case, Pevensey, in historic times, has been 
banked out from the sea by three-quarters of a mile of added 
land.2 Mr. Drew, in the memoir quoted, shows how any 
obstruction that may be run out into the sea will cause an 
accumulation of the pebbles, which travel up the bay past 
Dymchurch from the south and west. The grand line of 
pebbles that forms the Chesil Bank, connecting Portland 
and the mainland, may thus have arisen by the occurrence 
of an obstacle in the form of a clay-bank, which rises there 
to about the level of low water.^ At present there is room 
for a road and a railway along this singular accumulation. 

Now let us walk north from our fishing-village, over the 
low headland on that side, and down upon the flatter coast 
which catches every wind that blows. Wastes of sand, in 
which bent-grass grows at intervals, seem here piled upon the 
pebbly beach. These are the sand-dunes, which form such 
important barriers to many exposed portions of the coast. 

When we get among them, we walk with difficulty across 
the tumbled hollows ; and any eddy of the wind drives the 

^ F. Drew, ** Greology of Country between Folkestone and Rye " Mevnoirs 
Oeol. Surv. Ot. Britain, 1864, p. 18. 

- \Vm. Topley, "Geology of the Weald," p. 313. 
8 T. Oodrington, Oeol. Mag., 1870, p. 23. 



ALONG THE SHORE II3 

sand sharply in our faces. The curious long curves and semi- 
circular excavations in these dunes remind us of pictures of 
the African deserts. These heaps, forming actual hills in 
some parts, are being reshaped and quarried into by the 
swirls of the sea-wind. As a matter of fact, the wind has 
piled them up in the first instance. They are formed of the 
lighter material, the sand, which could be caught upand carried 
from the beach by the air-currents ; and to this day they are 
shifting and uncertain. Any little bank or line of obstacles 
causes a return gust as the wind strikes it, and a deposition 
of the sand takes place, parallel to and at a little distance 
from the front of the obstacle. The ridge so formed is added 
to almost daily on the seaward side, and parts of it are carried 
away, but more slowly, on the landward face. It becomes 
damp and compacted with the rain, and then quickly dry 
again, giving vegetation but little chance upon it ; and the 
bent-grass that somehow manages to exist only helps further 
sand to accumulate. We seldom see the base of the sharp 
green lances, as they struggle bravely against the drifts 
deposited between them. 

Sand-dunes have an unpleasant habit of encroaching 
upon the land, especially in regions of permanent winds 
from seaward. The unhappy cultivators of the fields in vain 
build walls and fences to check the advance. The wind, 
breaking on the wall, forms eddies, indeed, which drive back 
the slowly moviug sand-waves ; but the crest of the dune is 
continually being carried over the wall, and a copious sloping 
deposit is produced upon the farther side. 

Very often long promontories and hooks of wind-borne 
sand grow out across sea-inlets, as occurs at Portrane in 
County Dublin. The foundation is an ordinary sand-bar, 
where the meeting of waves and rivers causes a deposition of 
the material carried by both. The wind lays hold of this sand 
as it dries between the tides, and piles it up into irregular 
heaps. These in time grow larger, as additional sand is 
brought daily to the mass, and a hummocky unstable ridge 
results, perhaps forty or fifty feet above the sea, in the place 
of the wide flat sand-bank. 

Land-snails abound in most of these sand-dunes ; we can 
hardly walk without crushing them. Here and there, where 
a farmer has required sand for his buildings, a cutting has 
been made into the dune ; and we find that some of the 

u 



I 1 4 OPEN-AIR STUDIES 

lower layers are cemented into a friable kind of sandstone. 
The tiny shell-fragments from the beach, together with the 
broken snail-shells, have supplied the rain with calcium 
carbonate, and this has been deposited between the grains 
during the times of drying. Thus true sandstone may be 
constructed above water by atmospheric action only. 

It is a strange landscape, as we sit among these sand- 
hills, with their yellow slopes gleaming all along the northern 
bay, and the blue water stretching from them almost with- 
out a wave into the Channel. On the low land behind them 
the fields are all scattered over with the sand ; stronger air- 
currents might convert the whole region into a desert, only 
suitable to the rabbits which run in and out here beneath 
our feet. Away at one angle of the bay a low pebbly cliflE 
catches our eye, higher than the beach-terraces that are 
piled up during exceptional storms. It is clearly something 
different from the sand-dunes, which at that point have died 
away ; the sea evidently cuts into that corner at times, and 
no light sand is allowed to accumulate. Our last studies on 
this coast-line may conveniently be carried on out there. 

We have now seen how the shore is a thing of no fixed 
importance ; how, if you make a map on a large enough 
scale, you may find your work out of date from year to year. 
The sea seems to determine the shore-line, cutting away 
here, and depositing there ; and even our huge promontory, 
with its rampart 700 feet in height, seems destined to go 
down before it, and to be levelled to a pebbly waste. That 
small cliff over yonder, with the round stones sticking out of 
it, can, however, tell us a tale more surprising than any of 
the bluster of the sea. 

When we come up to it, it does not seem much to look 
at ; it is not very different from the storm-terraces of the 
beach below. But its top rises far above the level of any 
modem tides or tempest- driven rollers, and evidently forms 
a firm continuous plateau for some distance inland. The sea 
is, in fact, cutting it away at this point, and making a low 
cliff which extends north as far as we can see. This bed of 
old pebbles evidently runs for some miles up the coast. 

Our first idea is that it is an alluvial deposit, formed by 
the numerous streams which run down from the distant hills. 
But a layer of white crumbling matter attracts us — ^these 
are surely the broken edges of shells embedded among the 



ALONG THE SHORE I I 5 

gravels. (Compare Plate X.) We begin to dig in various 
portions of the cliff ; and soon we may disentomb a whole 
cluster of periwinkles, with flakes of cockle-shells, and oysters, 
and a scallop here and there, such as we may find below us 
on the existing beach. 

These shells have, however, lost their colour, and usually 
their outermost layers; they are in part decomposed, and 
are not exactly of a modem aspect. Yet we find the same 
species as still inhabit the Channel, though some of them 
may now occur farther north or farther south of our parti- 
cular stretch of country. We may even turn up these shell- 
fragments on the surface of the fields inland, where the level 
area ends against the hills, and where we may be fifty feet 
above high-water mark. Clearly we have here an old beach, 
a marine deposit, which the sea no longer covers. 

The sea, then, has shrunk away? That is possible, but 
it is not the simplest explanation. The sea is certainly held 
up against the edges of the land by the attraction of those 
masses which stand above its surface, e,g,, the great moun- 
tain-ranges along the coast, and, indeed, any prominent 
headland. Thus the mean sea-level is higher on any ordi- 
nary shore than it would be if the land were perfectly level 
with high-water mark. The sea, then, must shrink away, 
and the mean sea-level will be lowered, if denudation re- 
duces the level of these attracting masses; and we have 
seen that this reduction is steadily going on along our coast. 

But this will not be sufficient to account for what has 
here occurred. If we follow out our old sea-terrace, we shall 
find irregularities in its level ; at one point its top is fifty 
feet above the sea, but north and south of this it draws near 
to the sea-level in a distance of seven or eight miles. More- 
over, we may be fortunate enough to find that its seemingly 
level surface is in places sloped down as it stretches inland — 
the terrace has received a gentle tilt in that direction. When 
we have studied the older stratified rocks in detail, such 
evidence will seem to us quite natural. We shall then be 
quite ready to conclude that the land has been lifted, and 
irregularly lifted, above the sea. 

Such elevated marine accumulations are called raised 
beaches ; but we restrict this name to those in which the 
shells are of modern character and are mostly living in 
adjacent seas. When we find human remains or instruments 



I 1 6 OPEN-AIR STUDIES 

lying among the shells in such a beach, we conclude that the 
elevation took place after man had appeared upon the earth ; 
and there is no reason to suppose that such movements of 
the coast have come to an end at the present day. In Sicily 
beds of very modem marine shells are found 2700 feet above 
the sea ; ^ and in California recent shore-terraces, with the 
pebbles bored into by marine molluscs, occur at a height of 
1 240 f eet.^ Some of the occurrences of marine shells of living 
species at high altitudes in our own islands have been the 
subject of much controversy ; but, in the face of what we 
know to have gone on in other countries, it is not in any way 
improbable that the shores of the Irish Channel, for example, 
have been elevated some 1500 feet in recent times. The 
earth's crust heaves and moves beneath us in a series of slow 
but enormous waves. Standing against our raised beach, we 
can see how it defies, as it were, the destructive forces of the 
sea. Here, at any rate, new land has been made by a power 
which hitherto we had no thought of; and later, when we 
stand among the twisted strata of the Central Alps, we shall 
remember the evidence of modem elevation afforded by our 
pebbly coast.^ 

It is reasonable, however, to consider the contrary action 
— the land may in some areas be on the wrong slope of an 
earth-wave, and may be thrust down beneath the ocean. 
The western districts of the British Isles furnish us with 
interesting evidence that such has actually been the case. 
The maps of an ordinary atlas show how deeply indented the 
west coasts of Ireland and Scotland have become ; there is 
a general absence of wide and sweeping bays, such as we 
associate with sea-action, and in their place we have Qords, 
long winding inlets, penetrating perhaps fifteen or twenty 
miles into the land. In Norway this feature is developed 
on a far more striking scale, as any one who has painfully 
drawn the outline of the coast in his school-days knows full 

^ See De Lapparent, "Traits de Geologic," 3me ^dit., p. 1383. 

2 A. 0. Lawson, *' Post-Pliocene Diastrophism of Southern California," 
£uU. Depart, of Geology ^ Univ. of Calif omia^ vol. i, p. 127. 

3 A fine example of modern earth-movement, this time in connexion with 
an earthquake, was afforded in 1891 at Neo, in Japan. A line of fracture 
occurred 112 kilometres (67^ miles) in length, horizontal and vertical move- 
ment taking place along it. In places the ground on one side was raised 
20 feet, and the movement affected the hard underlying rocks as well as the 
alluvium of the surface (Milne, Burton, and Ogawa, " The Great Earthquake 
ia J&p&n, 1891^" plate xx ; and B. Kotd in Qeoi, Mag,^ 1894, p. 191). 



ALONG THE SHORE I 17 

well. But the Scotch examples of Loch Fyne, Loch Long, 
and the smaller but gloomier Loch Houm, are admirable for 
our present purpose. 

The walls of a fjord come down steeply to the water, and 
are continued similarly below. The narrow inlet, with its 
great depth of water, resembles a flooded ravine among the 
mountains. Often the mouth is shallower than some portion 
farther inland, the great Hardanger Fjord of Norway being 
about 190 fathoms deep at its entry and 440 fathoms in 
certain spots within; and the depth inside is not related to the 
depth of the outer sea. Loch Etive, one of the grandest of the 
British fjords, has an outlet not 3 fathoms deep, set with rocky 
islets ; but soundings give J6 fathoms off Port an Dobhrain, 
which is a good twelve miles up the inlet. Clearly hollows 
such as these cannot result from the battery of the waves. 

Sitting on the heathery brae-side above Loch Houm, and 
looking up to the rain-swept mountains of Glen Quoich, we 
see the fjord winding like a sheet of silver between the great 
masses of the hills. The wild flowers and ferns climb along 
the banks and touch the water's edge ; there is all the tran- 
quillity of a lake, and only in the seaweeds do we catch some 
suggestion of the sea. At the head of Loch Duich, again, in 
the purple highland of Kintail, the alluvial floors of Glen 
Shiel and Glen Lichd come down into the two arms of the 
water, and the sea-inlet is seen to be perfectly continuous 
with these valleys. In fact, fjords are nothing else than 
valleys lowered beneath the sea ; the rivers carved them out, 
and the sea was let slowly into them. Sometimes the moraine 
of an old glacier lay across the mouth and shallowed it ; some- 
times the bending of the earth was not regular, and the 
valley-floor was actually lowered to a greater depth than 
the sea-floor outside. On the flanks of many fjords, raised 
beaches can be seen, showing that a sort of see-saw move- 
ment has taken place, now of subsidence, now of elevation. 
This beautiful feature of a mountainous coast is due, then, 
to a sinking of the land into the sea ; and earth-movements 
have again been the chief factor in determining the coast- 
line. 

Outside the fjords there are generally numbers of islets, 
running in lines away to sea. These are the crests of partly 
submerged ridges, being in many cases merely the continua- 
tion of the valley-wall on either hand. Lismore, lying in 



^ 



I I 8 OPEN-AIR STUDIES 

the mouth of Loch Linnhe, is a ridge that formerly divided 
the greater valley from a smaller southern one ; the sea has 
entered both and has overflowed the col between them. To 
the west of the north-east point of Lismore the sea has a 
depth of 54 fathoms ; to the east, on the old col, it is only 
3 to 6 fathoms, with sand-banks gathered around projecting 
islets. The mountainous back of Jura is, again, the wall of 
a great valley, the opposite side of which is still seen in 
Knapdale and Kintyre ; and the island of Arran itself is an 
outlying block of the western flank of a valley that stretched 
from Galloway to the south foot of the Grampians near 
Dalmally. The channel to the west of Arran is a second 
roughly parallel valley, the col which once divided it from 
Loch Fyne being some 40 fathoms under water ; while the 
main valley to the east of Arran has its floor submerged 
pretty regularly to 80 or 90 fathoms. 

Glaciers filled most of these long hollows and kept them 
clear from dSbris, gradually shrinking away, as they have 
done in Norway also. At present the deltas of highland 
rivers are encroaching on the upper waters of the fjords, while 
the sea is depositing banks across their narrow mouths. In 
this way, as long as deposition is in excess of excavation, they 
may again become converted into valleys with flat alluvial 
floors. 

The study of fjords will lead us on and on to consider still 
greater features of the world. All round the British Isles 
accurate soundings have been made, and we know that we 
stand upon the edge of a great continental plateau, the 
western side of which drops steeply into the Atlantic. The 
line marking a depth of 100 fathoms upon our charts passes 
from the coast of Norway outside the Shetlands and the Outer 
Hebrides, runs from 25 to 100 miles distant from the west 
coast of Ireland, and then curves down to Biarritz and con- 
tinues on close against the Spanish coast. One hundred 
miles west of County Mayo, in Ireland, we reach a depth of 
as much as 1400 fathoms, and 300 miles west of Kerry we 
find 2700 fathoms, or more than 3 miles. Here, then, we are 
fairly in the ocean ; but the British Isles lie entirely to the 
east of it, and are in no way surrounded by it. 

If we return across Ireland, the channel between Stran- 
raer and Lame has a depression reaching 140 fathoms, and 
8j fathoms are found between Dublin and Holyhead. Gene- 



ALONG THE SHORE I 19 

rally speaking, the hollow between Ireland and England is 
only 50 fathoms (300 feet) deep. 

The English Channel, again, at Dover reaches 30 fathoms 
in a few local holes, and is mostly only 20 fathoms deep. 
The broad North Sea, but for a deep channel close to the 
Norwegian coast (160 to 300 fathoms), measures rarely as 
much as 50 fathoms. 

So that our islands may be regarded as distinctly Euro- 
pean, and an elevation of 600 feet would cause an extension 
of the continent as a broad north-western promontory, 
bounded by a reduced Bay of Biscay on the sol^th and the 
narrow Norwegian channel, above mentioned, on the north- 
east. The whole of the British Isles, including St. Kilda, 
would become parts of the mainland by such a movement. 
A uniform uplift of half this amount, of 50 fathoms or 300 
feet, would join Ireland to Wales by a tongue of land between 
County Wicklow and Merionethshire, would bridge the gap 
from Donegal to Argyll, and would leave a long salt-lake from 
off Lough Foyle to the south of Dublin. The English Chan- 
nel would be obliterated, and one could walk from any point 
on the east coast of England direct to any point in Denmark 
or in Holland. One or two little salt-lakes would alone 
remain of our southern and Eastern English seas. 

The similarity of the wild land-animals of the British 
Isles to those of the Continent shows that a connexion 
must certainly have existed in comparatively recent times. 
Moreover, Ireland possesses some twenty-one species of mam- 
mals, Britain has forty species, and Germany as many as 
ninety. Allowing for the fact that certain species may have 
been killed off by their enemies in the restricted space of 
an island more easily than on a continent, where they could 
freely come and go, yet these figures show that Ireland was 
cut ofif by subsidence from Britain while the latter was still 
united to the Continent. Species continued thus to reach 
England until some forty had arrived, and then this area was 
also separated from the Continent. The westward migration 
of mammalian forms was thus checked by the Straits of 
Dover, which since then may have undergone many modifi- 
cations, both in width and outline. 

Numerous traditions of sunken land occur, pointing to 
a former extension of the British group of islands westward 
of their present boundaries. The fjords are all upon 



I20 OPEN-AIR STUDIES 

the Atlantic coast; and the steep little cone of Rockall, 
some 200 miles west of the Outer Hebrides, and the sub- 
merged Porcupine Bank, 150 miles beyond the Galway coast, 
yet coming within 85 fathoms of the surface, are doubtless 
relics of the ancient European border. An island, Hy Brasil, 
is shown in about the position of the Porcupine Bank on a 
French map of 1640,^ and I have found it marked even on a 
chart showing Nelson's voyages, which was published in 181 5. 
The real date of its disappearance remains uncertain. 

Thus, as we walk back to the white houses of the fishing- 
village, and again look away over the curve of the bay, to the 
great cliff dominant beyond, we realise more than ever the 
shifting nature of the line where the land meets the sea. 
Not only does the water wear back the coast, and thrust itself 
away at other points by building ramparts of pebbles and 
sea-sand, but forces more mysterious and far-reaching are at 
work, elevating the whole border of a continent, or letting 
the sea into the complexities of its denuded surface. What 
we call the coast is a line of uncertainty and oscillation ; and 
the rocks which border on it can surpass the oldest fisherman 
in the harbour, in telling us strange and eventful stories of 
the sea. 

^ W. Frazer, " On Hy Brasil," Joum, Boy, Oeol, Soc. Ireland, vol. v. p. 
128. As to the traditional '* sunken land of Buss," between Greenland and 
Rockall, see G. C. Wallich, " The North Atlantic Sea-Bed " (1862), pp. 63-69. 



CHAPTEE V 

ACROSS THE PLAINS 

A FLAT country offers comparatively little attraction in 
itself, but derives most of its beauty from the expanse 
of air and sky. Beauty it certainly has, but of a kind 
so vast and indescribable that one has to live in the midst 
of it to feel its full meaning and its force. The greatness 
of the level finally comes home to one, especially if some 
well-known range of hills looms faintly into sight, forming 
a mere thin blue band on the farthest rim of the horizon. 
The landscape, as we move through it, is breathed in as a 
whole ; where the details are all so much alike, they all 
seem equally insignificant. 

The Fenland of eastern England is one of these great 
expanses, which at first seem almost wearisome, even to 
the bicyclist who skims so easily across them. Prom Cam- 
bridge northward to the estuary of the Wash, there are 
forty-five miles of level ground, with thirty or so more if 
we cross the inlet at Posdyke and penetrate the heart of 
Lincolnshire. Between the scattered villages lie areas of 
black peat, covered with coarse grass and dug into here 
and there for fuel. The roads are carried along the crests 
of broad embankments, with dark little drainage-cuts on 
either side of them, crossed by bridges to the fields. A 
few trees cluster round the old farm-houses, protecting 
them from the winds that sweep across the fenland steadily 
for weeks together, now chill and biting from the eastern 
sea, now stronger and moister from the west of England 
and the Atlantic. The sky is usually full of great cumulus- 
clouds, dark grey below and silvery white above, where the 
sunlight strikes through them in long shafts across the grey- 
green plain. A church-tower or a windmill is visible ten 
miles away, when touched on by these sudden gleams ; then 
it sinks back again into the great gloom of the horizon. 
Far in the south the hills beyond Cambridge may be visible, 



121 



122 OPEN-AIR STUDIES 

with dark woods and a few yellow fields, shining in a clearer 
air. There is an aspect of thunder across the fenland all 
the summer ; yet the rainfall is one of the smallest in our 
islands. 

Long lines of pollard-willows follow the courses of the 
streams. The main rivers have mostly been *' corrected," 
to prevent the flooding of the lowland, and to make them 
serviceable for boats ; and high artificial banks confine them 
in straight lines across the country. The currents of some 
of these rivers flow rapidly enough, and all are thick with 
sand and fine brown mud, which they deposit in long 
alluvial banks as they enter the North Sea. The changes 
in the form of the coast, due to this deposition, have been 
very noticeable around the Wash ; but a large part of the 
material there added appears to be mud swept by marine 
currents from the south-east promontory of Yorkshire.^ 

The fine sandy mud brought down by the rivers can be 
easily seen at low tide near their mouths. The Glen and 
the Welland unite west of Fosdyke, and have constructed a 
flat of compact material in what was once a broad sea-inlet. 
In the narrow channel remaining, each rising tide produces 
a rapid inflow of sea-water, entirely reversing the current 
of the stream. Much of the suspended matter is thus 
brought back again from the sea itself, together with fine 
marine mud or silt, and these are spread over the alluvial 
flat, when the tide is full and overflows it. Between the 
action of the river and the sea, the land is growing slowly 
outward into the Wash. In John Gary's map of 1822, 
prior to the Ordnance Survey, the sea is shown forming an 
inlet three miles long and a mile wide west of the present 
mouth of the River Welland. The old Gross Keys Wash, to 
the east of Holbeach, has similarly disappeared, the estuarine 
deposit having risen high enough for the sea to be artifi- 
cially banked out and the whole inlet to be reclaimed. 

Numerous lakes or meres formerly existed in the fenland, 
notably Whittlesey Mere in the county of Huntingdon ; 
these have been drained by their owners, and have ceased 
to break the monotony of the plain. But traces of many 
lakes of far older date are found among the deposits of this 
area, and were no doubt destroyed by slow alluvial infilling. 

^ H. B. Woodward, "Geology of England and Wales," 2nd edition, 
P- 5^9' 



ACROSS THE PLAINS I 23 

Thus fresh-water shells are found in some of the fenland 
sections, between layers of clay and peat ; while plant-beds 
and lignite bands show the former prevalence of an approach 
to forest vegetation. Stumps of oak, yew, and fir have 
been found beneath the peat, which seems to have spread 
over the previously wooded ground when a general lowering 
of the temperature of the district was in progress. The 
brown and black product known as Peat resulte from the 
decay of humble closely growing plants, and notably of 
certain mosses,^ which love damp surroundings and a tem- 
perate climate inclining towards coldness. The general 
evidence of the deposits of the East Anglian plain shows 
that sea-beaches, sands, and gravels extended at first far 
over the present land. Mr. Skertchly writes ^ that the bay 
of the Wash ** was once coextensive with the Fenland itself, 
and 1300 square miles have become dry ground within 
recent geological times, and the process is still going on." 
The rivers filled up the bay at one end, and forests and 
peat-bogs spread upon the delta ; the sea silted up the 
outward face, where the incoming tides, laden with sus- 
pended matter, met the currents from the land. When the 
deposits had reached high-water level, vegetation sprang up, 
as it does now, on these marine banks, and not only com- 
pacted them, but caused further deposition as every spring- 
tide overflowed them. In places the sea may have again 
gained upon the land, through local subsidence of the soft 
and yielding masses in the estuary ; the marine sands and 
ancient silt!, found in drainage-cuts and borings, prove 
their origin by containing such shells as the common cockle 
and the periwinkle. Thus our East Anglian plain must be 
regarded as a complex delta, produced by numerous rivers 
flowing mainly from the south-west; the sea has assisted 
in its own defeat, and the land is still growing in a north- 
easterly direction. Those portions of the alluvial area which 
are of a sandy or gravelly character have long been available 
for habitation ; the peat has already ceased to spread, under 
the influence of the return of a milder climate and of active 
drainage-operations ; and the seaward front of the delta has 
been steadily reclaimed by artificial banks erected from the 

* Hypnum Jluitans, not Sphaf/num, is the common species in the Fenland 
peat (Miller and Skertchly, "The Fenland," p. 555). 
2 Miller and Skertchly, Ibid.y p. 224. 



124 OPEN-AIR STUDIES 

times of the Bomans to our own. But the plain would have 
gone on extending, only more slowly, without human inter- 
vention. 

Thus even this placid country, the old Bedford Level, 
the Isle of Ely, is, with its many water-ways, in a state of 
uncertainty and unrest ; parts of it are scoured out by the 
streams as they come in haste out of the hills; and the 
material, with that brought from longer distances, is de- 
posited again elsewhere along the continually changing 
coast-line. Our enquiry into the Fenland shows that we 
are merely dealing on a large scale with the features shown 
clearly to us in the estuary at our little fishing-village 
(p. 90), combined with those seen in the broader portions 
of the river-valley in Tyrol. 

This strangely impressive plain of England gives us all 
the broad effects of Holland, without the trouble of crossing 
the North Sea. Holland is a country formed out of the 
delta of the Bhine, and the materials supporting its in- 
dustrious towns may have once formed part of the Alpine 
ridges some 800 miles away. The coast is constantly in a 
fluctuating state, and large areas have sunk nearer to or 
even below sea-level in historic times. The drying and 
compacting of the deposits, assisted by artificial drainage, 
has caused some part of this subsidence; there is probably 
also an oozing and a flowing out seaward of the lower beds 
of sand, which thus produces a sinking of those which have 
been in later years piled on them.^ 

Sedgemoor, in northern Somerset, supplies to dwellers 
in the west of England an admirable picture of an estuarine 
plain. An old narrow promontory, with a road carried along 
the summit, divides it from the alluvium of the Biver Brue, 
which fills a valley reaching nearly to Cheddar. On crossing 
the back of the Mendips and looking down on Wells, we see 
this plain of the Brue stretching away to our right, with the 
island of Brent Knoll standing in it, and the steep cone of 
Glastonbury Tor rising like a volcano near its eastern margin. 
If we push on to the south, and cross the promontory above 
the quarrying-village of Street, we see the second infilled 
estuary, with the Biver Parret and its tributaries winding 
among a number of artificial drainage -ways. Here also 
there are small hills rising like islands from the plain, and 

^ SuesB, ** Antlitz der Erde,'* Band ii, p. 531, &c 



ACROSS THE PLAINS 12$ 

the villages, Weston Zoyland and the rest, are quaintly 
perched upon them. One historic spot, a steep cone utilised 
as a fortress in ancient days, still bears a suggestive name, 
the Isle of Athelney.^ 

These rivers, descending from the southern termination 
of the Cotteswolds, have, in fact, choked an old sea-inlet, and 
have piled their alluvium, layer by layer, until it has almost 
swallowed up the islands. On digging through the peat 
round these projecting masses, beaches of marine sand are 
found ; and the shells in them are those of common living 
species. The waters of the Bristol Channel have only been 
driven out during the last two thousand years, or since the 
Romans came into the country. 

Let us now proceed to cross more spacious plains ; they 
also can tell us their own history. 

In the north of Italy a great level surface stretches for 
3CXD miles, from the Alps of Piedmont beyond Turin to the 
mouths of the Po near Venice. It is continued north-east- 
ward for another eighty miles to Udine and the Austrian 
frontier ; and here, in a more open and uncultivated country, 
we may study its details most conveniently. Away west, 
by Milan and Chivasso and Turin, the earliest tributaries of 
the Po come down from the St. Gotthard, Mont Blanc, and 
Monte Viso, and suflSce to flood the whole level country 
during a rainy spring or autumn. Up here above Venice 
we have an independent set of streams performing the same 
actions, and this north-eastern prolongation will serve as a 
model of the whole Italian plain. 

We have already mentioned the Valle del Perro (p. 65) 
in the Venetian Alps, with its cataract of a river, its vertical 
rock-walls, and its sudden windings which seem from point 
to point to close the gorge. When we emerge from it at 
the hamlet of Resiutta, we see the pebbly banks stretching 
out into a wider valley — deposition of the suspended matter 
has already commenced. Soon the Pella, which is cutting 
the ravine, is joined by the Tagliamento from the west, 
and the two rivers meet in a barren wilderness of stones. 
Alluvial islands begin to appear among these broader waters ; 
but the torrents in flood-time still carve their way from 

^ For a general account of this district, see H. B. Woodward, ** Geol(^y 
of East Somerset and the Bristol Coalfields," Memoirs Oeol. Surv. (1876), 
p. 145. Details of changes at the mouth of the Parret are given ibid, p. 159. 



126 OPEN-AIR STUDIES 

side to side of the valley, and are continually altering the 
features of its floor. Here on our left a side-stream comes 
down from the Julian Alps; it is so feeble in summer as 
to be hardly visible ; much of it trickles away beneath the 
banks of stones. But it has brought down, and still is 
bringing down in rainy seasons, a vast mass of pebbles, 
which it spreads out in a huge fan. The whole lower slope 
of the mountain is covered with this deposit, and two or 
three villages find room for themselves and their vine- 
terraces and their maize-fields along its lower margin. The 
shifting and steeper part of the detrital cone has to be aban- 
doned to the caprices of the stream; and up above, at the 
mouth of the lateral ravine, a red tower, with fantastic battle- 
ments, holds the narrow passage through the mountains. 

It is a landscape of sudden contrasts, and the alluvial 
fans, here broader and more nearly horizontal in their 
bedding than any we have seen in higher regions, are clearly 
swallowing up the older features of the range, and are pro- 
ducing a uniformity of slope and surface. 

These ridges amongst which we are still travelling, form- 
ing the outlying parallels of the central mountain-range, 
have been expressively styled foot-hills ; and they are literally 
being buried in the mass of detritus provided by the denu- 
dation of high altitudes. By a fairly abrupt transition, we 
pass from the foot-hills to the plain. 

On all sides of us now the level landscape stretches, with 
a cloudless sky above and a still hot air below. In half-an- 
hour or so we have forgotten the nearness of the Alps ; but 
we are still some 300 feet above the sea, and the rivers have 
an active flow. Along their banks we can perhaps read the 
story of the plain. 

Before we cross one of these rivers, the white villages, 
and the maize-fields, and all the life of harvesters, and 
brightly dressed women spinning as they walk, and sleek 
brown oxen drawing low-wheeled carts, vanish utterly away. 
Rough vegetation, such as bounded the alluvium in Tyrol, 
prevails for a mile or two across irregular pebbly banks and 
islets; the roads and railways are carried on viaducts of 
fifty or sixty arches across streams of the most insignificant 
character; and, finally, we come to the main river, and 
then have to repeat the passage of a wilderness upon the 
other side. 



ACROSS THE PLAINS I 27 

East of the old walled town of Udine, which is built 
upon a tempting hill amid all this flatness, the Torre and 
its tributaries come down through such an array of stones 
that the course of these rivers cannot be set down upon a 
map — only the broad pebbly banks can be indicated, stretch- 
ing southward towards the sea. West, again, of the wan- 
dering reaches of the Tagliamento, there are similar wastes 
in which the Cellina and Meduna are literally lost over 
courses of seven and ten miles respectively, their waters 
reappearing as recognisable rivers near Pordenone. The 
Tagliamento, moreover, has lifted itself in places on its own 
alluvial deposits, until it flows on a broad ridge thirty feet 
above the ordinary level of the plain (compare p. 69). 
Farther west still, the magnificent Kave, which runs at San 
Stefano and Auronzo through one of the grandest ravines 
in Europe, degenerates into a vagrant group of streams, 
expanded and divided over a breadth of two and a half 
miles. If we follow all these rivers down across the level 
to the Adriatic, we find them terminating in marshy deltas, 
enclosing backwaters and salt lagoons. On an exaggerated 
scale, it is the same type of landscape that we have already 
visited (p. 8S) at the Brenta mouth near Venice. 

Our studies of the junction of side-streams and main 
streams in the mountains now come back to us, with a far 
wider meaning than we could have guessed as we wandered 
down our upland valley. The whole plain results from the 
uniting and overlapping of exceedingly flat cones of detritus, 
which become less clearly bounded, more unstable at their 
edges, as they leave the limits of the hills. The beautiful 
steep-sided cones of upper regions, at the foot of gaps in 
vertical rock-walls, become caricatured, as it were, by the 
broad triangular areas of pebbles lying on the gentle slopes 
of the foot-hills. Two or three of these expanded cones 
meet along the lower parts of their lateral edges, and over- 
lap on one another, according as one or other grows more 
rapidly. Their front margins push forward regularly into 
the open valley, or into the waters of some lake, which is 
thenceforth doomed. Here we have a picture in little of 
the growth of the Italian plain, formed by cone uniting with 
cone, delta with delta, all spreading outward into the con- 
tinental valley of the Adriatic. 

On the north side of the Alps, this enormous extension 



128 OPEN-AIR STUDIES 

of detrital banks is almost equally apparent. Much of the 
original deposition, on either flank of the chain, is no doubt 
attributable to the glaciers, which at one time formed their 
terminal moraines much farther north and south than at the 
present day.^ But the plains, as we know them, are the 
outcome of the distributing action of mountain-rivers, work- 
ing their will upon the old moraines, and also continually 
adding new fluviatile material. 

The area covered by detritus on the north stretches from 
the Lake of Constanz to Salzburg, and northward nearly to 
Passau, and is bounded by the steep banks on the farther 
side of the Danube as we return west by Regensburg and 
Tuttlingen. Ridges and valleys have been carved out in 
this region, but here and there it preserves the character of 
a plain. The period of extensive deposition is past, and the 
Alpine streams now cut down, for the most part, through 
the alluvial pebble-beds, and expose far older layers below — 
layers that were formed prior to the Alps themselves. 

As we climb out of the Inn valley near Innsbruck and 
cross over into Bavaria, we find ourselves on a plateau 
sloping gently northwards, with numerous streams running 
towards the Danube, which lies some ninety miles away. 
The forests soon give place to a more open country, which 
still falls regularly towards Munich. We can look over 
this gentle slope uninterruptedly into far blue distance, 
each village, with its church-tower surmounted by a bulb, 
standing out conspicuously along the pebbly road. It is 
a striking contrast after the dense fir -woods that we 
have just quitted, in which, perhaps, rain was falling and 
mountain - clouds were wandering; and the farm -lands, 
catching the sunlight, with little cottages, and sheltering 
copses, and long green hedge-rows, remind one of rural 
England, and are none the less delightful. In the great 
plain before us, everything is covered deep in drifted 
pebbles; the outermost ridges of the foot-hills have been 
worn down and buried, and we descend on Munich over 
the surface of a vast alluvial cone. 

The Isar is at this point the most prominent river ; but 
no less than twenty-two respectable streams, all running 
north or north-east, conspire, with their tributaries, to shift 

* See Penck, Bruckner, and Du Pasquier, "Syst^me glaciaire des Alpes," 
Bull. Soc, Set, not. de Neuchdtd, tome xxii. 



ACROSS THE PLAINS 1 29 

the pebbles of the plain, to sort them out and rearrange 
them, in the area between HohenzoUern and Upper Austria. 
The flow of the Isar is in itself surprising. If we approach 
Munich from the Danube, we climb up and down over 
small hills hidden in alluvium, and come at Freising upon 
the broadest area of the valley. The road ahead seems 
absolutely level, and right and left for some six miles no 
semblance of a hill is to be seen. But if we get across by 
the rickety little foot-bridges, over all the side-streams 
and back-waters, to the Isar itself, we find a cold green 
flood rushing between its pebbly banks, swirling round 
every obstacle in genuine waves, and looking like a moun- 
tain-torrent that has somehow got into the wrong surround- 
ings. The peasants have built walls of masonry to prevent 
its encroaching on the fields, and an area more than a mile 
wide is often abandoned to it as a playground. The fall is 
still about ten feet in a mile, and the surface of the plain, 
which was formed by the union of the river-cones in ancient 
times, is here becoming cut into by a shallow valley, in 
which lakes and alluvial flats have no doubt again and 
again arisen. 

Far in the north, the Danube runs under a band of 
steeply descending hills, and makes a great curve from Ulm 
to llegensburg, and then down again to Passau. The edge 
of the plain here coincides with a great line of fracture and 
movement in the earth's crust,^ and the river is thus brought 
against a wall of hard old rocks, such as the Bavarian Forest 
ridges, which lie on the up-side of this line of movement. 
The floor of solid rocks underlying the alluvial plain is 
believed to have sunk, or to be on the down-side of the line. 
But this would not alone account for the great swing of 
the Danube towards the north. It looks as if this river 
had been steadily thrust away iu that direction by the 
encroachment of the alluvial fans from the south, their thin 
edges pushing forward and spreading the plain - country 
into the very centre of Bavaria. At present the Danube 
has been pressed up against the solid northern wall, and 
can only shift farther by cutting into it at the base. In 
recent geological times it has been able to carve out a 
picturesque gorge between white limestone cliffs near 
Regensburg; and any undermining action now exerted 

^ See Suess, " Antlitz der Erde," Band i, p. 253. 



130 OPEN-AIR STUDIES 

against the northern masses will allow the plain to go on 
growing. 

A river working thus against one side of its valley 
imitates the horizontal cutting of the sea ; it may shift its 
bed constantly sideways in one direction, and the alluvium 
brought by itself and by its tributaries will form a flat of 
steacfily increasing dimensions upon the other side. The 
Danube plain at Straubing is thus quite a one-sided 
structure ; in the north rise the beautiful fir-clad ridges of 
the Bavarian and Bohemian Forests, the lowest foot-hills of 
which have been cut into by the river and have formed 
a band of yellow cliffs. On the south side the country 
seems absolutely level ; the towers of Plattling and Strau- 
bing are by far the most interesting objects in the land- 
scape; and the white road, made of the characteristic 
limestone pebbles, leads invitingly and easily to Vienna 
under the summer sunlight of the plains. 

There is, however, a more imposing spot in Europe from 
which to study the greatness of an alluvial plain. Let us 
come away by the railway into Hungary, across the corn- 
land of the Vag, and through the last narrows of the 
Danube valley to Budapest. The view from the old citadel 
south of Buda seems to open up all the east of Europe. 
In the north behind us we have the volcanic hills round 
Visegrad, the tumbled masses of the mining-country, and 
the far blue line of the foot-hills of the Karpathians; but 
south and east stretches the plain of central Hungary, with 
the grey-green Danube, some 400 yards in width, flowing 
through it in long sweeping curves. Ever since the river 
left "Vienna, it has tended to divide and to join itself 
together again, producing enormous elongated islands run- 
ning in the direction of the stream. Some of these have 
been carved out of the older alluvium, some have been 
deposited in the course of the present river ; and, were it 
not for human intervention, floods and redistribution would 
be the order of the day. 

The plain itself is richly fertile, and is now gradually 
becoming one of the great corn-producing countries of 
Europe. At sunset a warm pink haze settles across it, and 
gives even the cultivated portions the aspect of an un- 
touched prairie. Eough brown roads, worn by carts in the 
surface-soil, connect the hamlets of one-storied houses ; and 



ACROSS THE PLAINS I31 

here and there a little market-town straggles, its streets 
four times as wide as Piccadilly. In a Hungarian village, 
there is often room for a water-course on each side and 
another in the centre of the highway; and the country- 
roads have no true edges, but wander on and widen out, 
as if worn by some horde of Asiatic invaders on the march. 

On the edges of the plain the ground rises gently towards 
the great curve of the Karpathians. The corn-fields are 
found running up as long brown strips over the slopes of 
rounded ridges, and at last come to an end against the blue- 
green fir-woods on the mountains. These ridges and hillocks, 
deeply intersected by little dusty valleys, are the alluvial 
heaps banked against the solid mountain-side ; they are still 
being added to, but the streams in summer are liable to 
dwindle entirely away. Great boulders stick out of the 
banks of yellow earth, as records of former floods and torrent- 
action ; and a change of climate, such as might be produced 
by an increase in the elevation of the Karpathians, would 
speedily wash away these accumulated foot-hills and add their 
materials to the plain. In the great plain itself, stretching 
for some two hundred miles from side to side. Professor Suess 
believes that we have an area which has sunk in olden times, 
leaving the mountains standing about it almost like a ring. 
In such a gathering-ground, with its narrow outlet on the 
south-east, the phenomena of the Bavarian plain have natu- 
rally been repeated. Whether a lake ever filled the basin is 
a matter of opinion ; for the general flatness of the alluvium 
might easily be produced by the spreading action of the rivers. 
Von Eichthofen ^ shows us how the fine dry clay of the Hun- 
garian plain, with remains of fresh -water and terrestrial 
shells, has become carried up the slopes of the mountains by 
the wind, and has been deposited as a thick coating over the 
surface. The same observer records sand-dunes,^ forming 
characteristic wave-like ridges from north to south across the 
country ; wind-action has doubtless done much in the distri- 
bution of the fine materials. 

On so incoherent a surface, the rivers have naturally 
wandered and shifted at their will.* The Tisza (the Theiss 
of the Germans) is a remarkable example ; in the central 
part of its course, near Szolnok, it is working its way west- 

^ "China," Band i, p. 157, &c. - Ibid.j p. 159. 

^ See Reclus, "Nouv. Gdographie universelle," tome iii, p. 313. 



132 OPEN-AIR STUDIES 

ward at the rate of about one foot a year, so that, if a good- 
sized house were erected on its banks, the river would walk 
through it in little more than thirty years. It is thus con- 
tinually cutting into its crumbling western bank, and thrust- 
ing back the adjacent towns. The tributaries from the east 
bring in fans of detritus, which encroach on the main stream, 
as those from the Alps have encroached upon the upper 
Danube ; and the result is that this part of the river has 
shifted westward some sixty miles from the fringe of the Tran- 
sylvanian hills. Farther south, however, its shift is easterly. 
Trajan and Diocletian erected forts on a plateau on the east 
bank of the Tisza, close to its junction with the Danube, to 
prevent the Dacians from crossing ; in later times, this plateau 
became an island, and it is now on the west bank of the river. 
A similar case of Nature's taking matters into her own hands 
is recorded by Eeclus^ of a village in the alluvium near 
Speyr, which stood on the right bank of the Rhine in 1 570, 
and is now, against its will, upon the left. 

The Tisza leaves behind it, on one side or the other, dead 
loops and deserted back-waters, which form curiously curved 
lakelets until they finally become marshy and dry up. The 
substances held in solution by the river become concentrated 
by evaporation of the water, until the residue in the marshes 
is often salt ; and, on the final disappearance of the marsh, 
these salts become added to the alluvial matter of the plain. 

Similar abandoned portions of its course may be seen 
beside the Danube itself near Mohacs, and they are common 
along the Drau (or Drave), where it forms the frontier of 
Slavonia. An amusing result of such shifting in the soft 
alluvium of the plains occurred in the summer of 1894 on 
the borders of Galicia. Since 1892 disputes had disturbed 
the village of Kudrenice, owing to the movements of the 
River Zbrucz ; and commissioners had finally to be appointed 
to determine how far Russia and Austria were to be inter- 
changed at the pleasure of this animated frontier-line. So 
that even politicians cannot sit down in perfect certainty to 
decide for ever the boundaries of an empire. As we shall see 
later, even a range of mountains may grow, move forward, 
and outwit them. 

North of the granite knots of Central Europe, north of 
the Fichtelgebirge, the Bohemian ranges, the Sudetic, and 

^ "Nouv. Q^ograpbie universelle," tome iii, p. 550. 



ACROSS THE PLAINS . I 33 

the Karpathians, there is a great plain which extends as far 
as the Baltic, and away into Russia on the east. The abun- 
dant glacial detritus forming its foundation, drifted originally 
from the north, opens large questions which cannot be entered 
into now. We are concerned here rather with its present 
aspect and condition. Ranges of old hills rise here and there, 
partly buried in the alluvium ; and the greater part of the 
plain is occupied by a fine-grained clayey deposit known as 
Loss. The distribution of this material has been aided by 
rapid flooding of the lowlands during periods of general dry- 
ness ; in such a climate the surface becomes dusty and broken 
up, and any rain quickly washes down the finer matter from 
the hillside taluses and spreads it out in the floor of tem- 
porary and very shallow lakes.^ These dry up again, and the 
wind acts upon the surface, carrying the tiny particles for- 
ward, and covering hills and dales alike with the unstratified 
deposit. The shells of land-snails, particularly of a species 
preferring moist and cool places (Succinea ohlonga), are abun- 
dant in this loss, which is typically a structureless calcareous 
clay. The sands associated with it are often blown into 
dunes, as in the Hungarian plain. In Austrian Poland, near 
the Russian frontier, one may travel for miles through a level 
country, which a few rainless seasons would soon convert into 
a desert. The heather manages to hold its own here and 
there, and irregular clumps of fir-trees secure a footing. But 
the ground between them is frequently bare, loose, and wind- 
tossed, and the yellow sand is visible even round the exposed 
roots of the trees. The whole of this strange and shifting 
landscape gives one the impression of two rival forces strug- 
gling for the mastery. 

Von Richthofen urged most forcibly the importance of 
wind-action in producing loss, in his memorable work on 
China before referred to.^ This unstratified yellow calcare- 
ous clay, full of the little tubes left by decayed rootlets, 
light and porous, drying on the surface almost as soon as the 
rain ceases, has filled up vast depressions in the interior of 
China and has climbed high upon the flanks of mountain- 
chains. The waters that soak into it have cut deep vertical 
clefts, which are often produced by the falling in of the 

^ See I. C. Russell, *'Subaerial Deposits," Oeol. Mag., 1889, p. 343. 
^ "China," Band i, p. 56, &c. ; and "On the Mode of Origin of the 
Loess," QeoL Mag., 1882, p. 293. 



134 OPEN-AIR STUDIES 

material above the courses of underground streams. The 
landscapes in the plains that are formed by the infilling 
action of the loss are thus of a most singular character, and 
the trade-routes of the caravans often lie along the bottoms 
of canons, which may be only four to six feet wide. Von 
Eichthofen points out that in rainless deserts fine dust may 
be formed by the cutting action of blown sand acting on the 
face of rocks ; but this material is carried away by the gusts 
almost as soon as it is formed. Wind-borne dust, and con- 
sequently loss, only accumulates where vegetation already 
exists ; it becomes caught in the twigs and little branchings 
near the soil, and adds to the mass of the plain. Year by 
year the vegetation rises to a higher level ; the plain is 
growing under it. Heavy rains would wash off this accumu- 
lation ; and hence a fairly dry, but not a desert, climate is 
required for the production of true loss. At present, in 
China, a period of denudation by rain and rivers has set in, 
and the loss is being cut into and removed. 

The formation of loss depends largely upon the materials 
supplied to the rain-waters and the steady wind-currents. 
M. de Lapparent,^ who believes, in spite of Von Richthofen's 
arguments, that the loss is the result of the action of heavy 
rains and of alluvial deposition, shows how the sandy clays 
of the north of France have become broken up to form loss 
in the same region. A happy combination of the alluvial 
theory with that which attributes the distribution to the 
wind will allow us to perceive (p. 133) that a country where 
river- muds or loose delta-deposits occur high and dry will 
be exactly that most suited for the supply of loss-materials, 
which may then be carried far away, or may be redistributed 
over the inequalities of the old river-beds near to their place 
of origin.2 

We may now profitably glance at the extensive deposits 
in the north of India,^ where a combination of such features 
has actually been at work to produce the plains. These 
deposits cover 300,CXX) square miles, with the three great 
rivers, the Ganges, the Brahmaputra, and the Indus, wander- 

^ " Traits de G^logie," 3me Mit, p. 1373. 

^ See the carefal discussion by W. F. Hume, Oecii. Mag., 1892, p. 549, 
and 1894, p. 306. 

^ ''Manual of the Geology of India; Stratigraphical and Structural/' 
^A)l. Swv, India, 2nd edit., p. 427, &c. 



ACROSS THE PLAINS I 35 

ing through them and spreading them seaward on both sides 
of the peninsula. The loops of the Ganges might easily in- 
tersect those of the Indus across this huge alluvial level, and 
so change the drainage of thousands of square miles. The 
material of the plain is a sandy clay, often cemented in 
an irregular lumpy manner by carbonate of lime. In a zone 
about thirty miles wide, extending along the foot of the 
surrounding hills, true pebbles occur, representing the ex- 
treme edge of the ordinary mountain-fans ; farther out we 
find merely sand and clay, the latter becoming very fine in 
the flatter portions of the plain. Fresh-water shells show 
that here, as in Europe, we have nothing to do with any 
incursion of the sea or with the uplifting of a " plain of 
marine denudation." The present surface is due to river- 
action, assisted in the less marshy portions by the wind. 
A well-known boring near Calcutta, finished in 1840, pene- 
trated fresh-water alluvium to a depth of 460 feet below the 
present mean level of the sea, which shows how depression 
of the first-formed layers has gone on steadily in the delta.^ 
At Lucknow a borehole has found no base to the series of 
river-deposits even at 1000 feet below the sea-level. 

At present the rivers seem less burdened with suspended 
matter than of old, and run in broad valleys excavated in the 
earlier alluvial flat. It is probable that, as the deltas become 
steadily silted up, and as their surfaces become raised by the 
additions made in times of flood, the flow of the rivers will 
be checked in their central portions, and deposition will take 
place in the broad valleys farther and farther up towards their 
heads. Thus the level of the older plain may eventually be 
restored.^ 

The geographical changes in a country so constituted may 
of course be as rapid as in Europe, and are on an altogether 
bolder scale. It thus appears that the mouths of the Brah- 
maputra and the Ganges are always struggling with one 
another ; while the Jumna, which now joins the Ganges, flow- 
ing through Agra to Allahabad, originally made its way across 
Bahawalpur to the western side of the peninsula. The dry 
bed of an old river is traceable along this route for a distance of 
nearly four hundred miles ; and it was probably not abandoned 
by the Jumna until after the Hindus were in the country, 

^ Compare p. 89. 

2 ''Manual Geol. India," 2nd edit., p. 446, 



136 OPEN-AIR STUDIES 

All these great plains that we have been considering con- 
tain salts, which sometimes render their surface-soils unfit 
for vegetation. We have already seen how the drying up of 
marshes has deposited part of these materials ; but in most 
cases the mere soaking in of rain-water accounts for their 
presence and accumulation. The rain, with its dissolved 
gases, attacks the pebbles and the minute mineral grains, and 
decomposes many of their constituents. The salts carried 
ofiE in solution sink with the water into the easily permeable 
alluvium ; but there is a constant oozing out and circulation 
of this underground water, and later rains may even fill up 
the pores of the whole mass and cause a diffusion of the con- 
centrated solutions that occupy the lowest levels. Thus the 
salts are in part brought again to the surface, and become 
deposited there between the grains, or as a white crust, when 
evaporation has done its work.^ Von Eichthofen regards the 
tubes left by the rootlets of former vegetation as of import- 
ance in allowing such complete penetration of the mass by 
water. The loss of China is rendered surprisingly fertile by 
this constant renewal of the salts in the surface-soil, in a 
happily moderated degree, and the stores accumulated below 
in bygone times show as yet no signs of exhaustion. 

The great deposits of salt in the world had, however, 
another and a more rapid mode of origin ; and this also is 
connected with the formation of a certain type of plain. 

In the States of Nevada and Utah, in North America, and 
extending into California and Oregon, there is a region known 
as the Great Basin, the rivers of which either drain into 
lakes which have no outlets, or disappear in sands before they 
can reach the ocean. This area includes about 2 10,000 square 
miles, and contains a number of plains. Even in its low- 
lands, it is typically a plateau-country, being usually 5000 
feet above the sea.^ The air of this high inland region con- 
tains on an average only half as much moisture as it could 
absorb before reaching its saturation-point (p. 37) ; and the 
rainfall is only ten inches in a year. Towards its south end 
the Basin sinks in places below sea-level, and layers of salt 
are here spread over the valley-floors. The Great Basin con- 
tains a dozen or more lakes, the largest of which is Great 

1 Von Richthofen, " China," Band i, p. 71. 

2 G. K. Gilbert, " Lake Bonneville," U. S. Geological Survey, Monographs^ 
j, p, 6, &c. 



ACROSS THE PLAINS 137 

Salt Lake, near which the famous city stands ; and round this 
body of water, eighty miles in length, a considerable part of 
the country bears the character of a genuine plain. 

The Great Salt Lake Desert to the west measures about 
eighty by forty miles, and has a level surface, with but few 
interruptions. Such mountains and bluffs as rise above it do 
so steeply, and seem so out of keeping with the general char- 
acter of the landscape that the older emigrants, passing across 
in waggons, spoke of them as islands and gave them cor- 
responding names. The plain has shallow depressions here 
and there, which are converted into lakelets after storms, 
but which soon dry up again, leaving a surface of com- 
pact pale yellow clay,^ with a deposit of salt around its 
margins. 

The plain as a whole is covered by exceedingly fine mud, 
impregnated with salts, until we reach its margins, where 
detrital fans have encroached upon it. The prevailing winds 
are from the west, and have piled up dunes against the flanks 
of the hills on the eastern side, illustrating Von Richthofen's 
theory of the transference and spread of loss.^ 

The Great Salt Lake itself rests as a mere film upon the 
surface of this plain, being only about fifteen feet deep. Its 
waters are very bitter in taste, and so saline that the early 
Mormon settlers used to say that from three barrels of water 
they could obtain one barrel of salt. In 1850 there were 
some 22 parts by weight of salts in every 100 parts of 
water; in 1869 the lake had increased in size, owing to 
greater supply of fresh water from the surrounding hills, 
and the salts were only 15 per cent. Results as high as 19.5 
per cent, have since been obtained by Dr. J. E. Talmage in 
1889. Sodium chloride is the most prominent constituent, 
both in the waters and in the dried salts, which frequently 
appear upon the surface of the plains like snow. On the 
cooling of the lake in winter, crystals of sodium sulphate 
are thrown down, and may often be gathered from the 
bottom. 3 

^ For an important account of these ** adobe " deposits, and a comparison 
with the loss, see I. Russell, " Subaerial Deposits of the Arid Region of North 
America," OeoL Mag.^ 1889, pp. 289 and 342. 

- Hague and Emmons, "Descriptive Geology," U.S. OeoL Exploration oj 
^oth Paralld, 1877, p. 466. 

^ For these and other points, consult Gilbert's fine monograph, above cited, 
which is enriched by a handsome series of illustrations. 



0^/^ 



138 OPEN-AIR STUDIES 

This remarkable salinity of Great Salt Lake is paralleled 
in certain seasons by the smaller Sevier Lake far away to the 
south, which actually dried up in the autumn of 1879. A 
salt-layer four or five inches thick resulted, formed of sodium 
chloride, sodium sulphate, and magnesium sulphate. The 
irrigation- works carried out in the valley of the Sevier Eiver 
had in this case diverted the supply of water. 

Some twenty-five miles south-west of Salt Lake City, 
there is curiously a fresh-water lake without an outlet, called 
Bush Lake, which is believed by Mr. Gilbert to have dried 
up in recent times, and thus to have deposited all its dissolved 
material. This layer of salts has then been covered by some 
stratum of mechanically suspended matter, and the lake has 
since been filled up again with fresh water from the hills. 
Utah Lake is fed from the Wahsatch Mountains, and flows out 
into Great Salt Lake, and is consequently fresh. 

How has 'the Great Salt Lake, however, become so con- 
spicuously salt ? We have already hinted that it is subject 
to changes in volume ; in the spring the water rises, owing to 
the melting of snow upon the mountains, and in summer it 
falls, owing to the evaporation from the surface. But larger 
changes are in progress, due to alterations in the local climate; 
and any slight increase in depth means, in so shallow a de- 
pression, the flooding of a vast amount of the plain. Thus 
in 1850 the lake covered 1750 square miles, and this was in- 
creased to 2170 square miles in the course of the next twenty 
years. At present the area is decreasing, evaporation being 
in excess of the supply. 

In studying such fluctuations, we begin to see how the 
salt has accumulated in the lake. Surely it must be due to 
the old outlet having disappeared, and to the fact that 
evaporation has served in its place to remove the continual 
additions of river- water. The salts, as in the marshes of 
the Hungarian plain, have thus been left behind ; and, but 
for occasional rainy seasons in the hills, the salinity would 
be steadily on the increase. 

But, further, if we examine the walls of the mountains 
beyond the long dreary miles of plain, we find that they 
are marked by horizontal terraces, and that they have been 
actually excavated along these levels, clifiEs being produced, 
as if by the waves of ancient seas. Beaches occur, sloping 
wn from these terraces, and sand-banks and bars of 



ACROSS THE PLAINS 



139 



vaiions forms are common (fig. 7). The "islands" of the 
Great Salt Lake Desert, when examined closely, resemble 
islands indeed, with similar terraces carved ont of them by 
the waves. The cliffs that are so snggestive on the monn- 
tain-flanks rise to a height of lOOO feet sonth of Salt Lake 
City, with long sand-spits stretching from uoder them into 
the plain. A long aeries of explorations in this district has 
proved beyond a donbt that formerly an enormons lake not 




Pio. 7,— Old Lakb-Terraobh ok the Salt-Lakb Abe4 op Utah— The 
Gate op Bbab Rivbr. (From "lake Bonneville," by G. K, Gilbart; 
by pennisaion of tho Director of the U, S. Geological Surrey.) 



only occupied the Salt Lake Desert, bnt ran on southward 
in broad inlets over the salt-strewn plains and valleys. This 
lost lake has been called " Lake Bonneville " ; it rivalled in 
area the inland seas of the northern States, being nearly as 
large as Lake Michigan ; ' for it was 346 miles long, and 
130 miles wide, measured from Salt Lake City across the 
western desert. The waters rose about 900 feet above the 
present level of the plain. 

' Gilbert, " Lake Bonneville," p, 105. 




I40 OPEN-AIR STUDIES 

The wave-cut terraces on the shores and on the former 
islets represent successive levels at which the water lay 
continuously for long periods. The area of sloping beaches 
from one terrace to another corresponds to a time of fairly 
rapid decrease or increase in the volume of the lake. It 
appears that Lake Bonneville had a notch in its northern 
walls, at the head of the Cache Valley, which was banked up 
by alluvium ; and, when the waters were once high enough 
to flow over this pass, the soft barrier rapidly gave way, and 
a flood poured out towards the Snake River, which rapidly 
reduced the level of the lake. The torrent in the outlet 
finally cut its way down to the underlying limestone rock, 
and here continued to flow over without materially deepening 
its bed ; a second zone of terraces, 375 feet below those 
formed at the highest level of Lake Bonneville, marks the 
shore-line of this later resting- stage of the lake. We even 
know that the area of the lake at this period remained fixed 
for a longer time than when it was at its highest level, since 
the lower series of wave-cut terraces is far broader than the 
upper, and the banks of accumulated detritus are far more 
massive.^ 

But finally the lake began to shrink away, until the 
basin became a closed one, the water no longer reaching 
to the outlet. As the water was removed by evaporation, 
the surface steadily sank, and the alluvial cones from the 
hillside-streams grew downwards and outwards over the old 
terraces and slopes. Whether the huge Lake Bonneville 
ever actually dried up is a matter that cannot be determined ; 
but probably the Great Salt Lake, Utah Lake, and Sevier 
Lake are the last relics of its grandeur. The salt-marshes 
that are formed everywhere in the depressions after rain 
show how the floor retains much of the matter once held in 
solution by Lake Bonneville, while Great Salt Lake remains 
as its concentrated and still liquid representative. The 
river-waters still flowing into the old basin of Lake Bonne- 
ville contain about .025 per cent, of material in solution, 
while Great Salt Lake contains, as we have seen, about 760 
times as much. 

Thus the wonderful level plain, so strikingly contrasted 
with the terraced mountains and the "islands," represents 
the old lake-floor ; it proves to correspond on a large scale 

' Gilbert, op. cit,, p. 127. 



ACROSS THE PLAINS 141 

to the little grass-grown flat-bottomed basins so often met 
with in the Alps. When we say that Lake Bonneville rose 
900 feet above Great Salt Lake, we only gain an imperfect 
idea of the true magnitude of its basin. The greater part of 
its floor has become covered with sediments, the outermost 
washings from the surrounding cliffs ; these have been 
spread out in level layers of fine mud and sand over the 
whole central area, pebble-beaches running out into the 
deposits from the shores and islands. Mr. Gilbert believes 
that the lake-alluvium reached a thickness of at least 2CXX) 
feet ; erosion at the present time cannot carry the material 
out of the basin, and it is merely raised by the wind into 
long dunes in drier areas, or flattened down and caked 
together in others by the casual showers of rain. The 
foundation-layers of this great mass of alluvium belong to 
a period of lake-formation when the boundaries of Lake 
Bonneville were not yet established ; the hollow began to 
be filled up in far earlier geological times, and the total 
deposit may reach a depth of several miles.^ 

Thus plains, graduating into salt-deserts, may arise by 
the total abolition of ancient lakes. At the present time 
the floor of the Lake of Geneva is extraordinarily and almost 
mathematically level, after we once get beyond the steep 
banks formed by the continuation of the alluvial cones 
beneath the water. This level surface of finely sifted 
detritus, free from the swirl of currents and from any 
erosive action, lies at a depth of about ICXX) feet (309.5 
metres) below the surface. 2 This figure reminds one curi- 
ously of the relations formerly existing between the Great 
Salt Lake Desert and Lake Bonneville. 

Mr. I. C. EusselP has described another ancient lake 
in the Great Basin, lying near the north-west frontier of 
Nevada. **Lake Lahontan" was nearly as long as Lake 
Bonneville, but contained a great pear-shaped island which 
largely reduced its area. Seven saline lakes still lie in the 
floor of it, which are believed to be produced by flooding 
of the hollows after the complete drying up of Lake 
Lahontan. One of these. North Carson Lake, twenty miles 

1 Gilbert, op. cit.y p. 99. 

2 Forel, "Le Leman," tome i, pp. 51 and 109. 

3 '* Geological History of Lake Lahontan," Third Ann, Report U. S. Geol. 
Surv.j 1883, p. 195. 



142 OPEN-AIR STUDIES 

long and twelve miles wide, has been known to disappear by 
evaporation, leaving for a time "a plain of saline mud" 
as a continuation of the area of fine clayey sediments which 
form the Carson Desert. The depressions of this area, like 
those of Lake Bonneville, are occupied by level deserts, 
which represent the alluvial infilling of the great lake; 
and salts are constantly accumulating in crusts upon their 
surfaces, being brought by circulating waters from the 
strongly impregnated sediments below. Sodium chloride 
(common salt) and calcium sulphate (which combines with 
water and crystallises as Gypsum) are especially prominent 
constituents of these dried materials. In a closed lake- 
basin, as Mr. Eussell points out,^ fed by ordinary river- 
waters, calcium carbonate will be the first material to 
separate out on the evaporation of the lake, since it is the 
most abundant and least soluble salt in the rivers ; then 
calcium sulphate will be deposited, and then, after the loss 
of almost all the water, sodium chloride, the chlorides of 
magnesium and calcium following even later still. Both the 
shores of Lake Bonneville and Lake Lahontan give, in their 
layers of friable or compacter fresh-water limestone, which is 
known as Tufa, ample evidence of the deposition of calcium 
carbonate from solution. Often this deposit acts as a cement 
to bind the grains together in the sand-banks. 

Another feature of lake-deposits is the formation of 
hydrated iron oxide or Bog iron ore. The iron is brought 
into the water by the rivers, being held in soluble combina- 
tions by the acids produced by the decay of land-vegetation. 
These compounds break up under the oxidising influence of 
the air, when carried into bogs and marshes, or into the broad 
and constantly circulating waters of a lake ; and an insoluble 
substance, brown rust, or hydrated iron oxide, is produced. 
This accumulates at the bottom round water-plants and 
pebbles and sand-grains, and sometimes even forms little 
spherical concretions, which become heaped together to form 
a workable ore of iron. Hence lake-deposits are typically 
reddened by this coating of iron oxide over the surfaces 
of their constituents; and nothing is commoner, when we 
attempt to work out the past history of an area, than to 
come across beds of rock-salt and gypsum, associated with 

^ Op. eU., p. 229. See also A. J. Jukes-Browne, " Handbook of Physical 
Geology," 2nd edit., pp. 243, 247. 



ACROSS THE PLAINS 1 43 

red clays and sandstones and conglomerates. Fresh-water 
shells may help us to form a true judgment as to the mode 
of origin of such strata ; but the very absence of evidence of 
marine life, and the mineral characters of the rocks, will 
prove that we are examining the floor-deposits of an evapo- 
rated lake. Along the railway between Larne and Belfast, 
such reddened strata, with gleaming interlacing bands of 
gypsum, form an admirably clear example ; and great beds 
of rock-salt are found in the immediate neighbourhood in 
borings in the same series of strata. 

Thus the study of modem plains has led us to the con- 
sideration of lake-deposits, with which they are so often 
associated. In conclusion, let us glance at one or two areas 
of evaporation nearer home. 

The Dead Sea, in Palestine, is almost too familiar an 
example. The region in which it lies is nearly rainless, and 
it has no outlet, although the Jordan is steadily flowing into 
it. The surface of the lake lies 1292 feet below that of the 
Mediterranean Sea, and the water is in places 1200 feet deep. 
A large body of water has, however, been removed by evapora- 
tion, the alluvial terraces in the Jordan depression occurring 
as high as 1 400 feet above the present surface. The mol- 
luscan shells (such as Melania tuherculata and Melanopsis 
Saulcyi) occurring in these old deposits show that the lake 
was originally fresh. ^ When it had shrunk to 600 feet above 
its present level, it deposited, as at Jebel Usdum, salt and 
gypsum in the clays and sands. New materials were brought 
into it ; it may have spread and again contracted ; and similar 
deposits occur on the promontory of El Lisan, 300 feet above 
the present surface. The lake as we now know it is devoid 
of animal life, except for some small fishes near the entry of 
springs at its southern end. Cubes of rock-salt and plates 
of gypsum are being deposited upon its floor, where the water 
is more saline than in the upper layers. Captain Lynch,^ of 
the American Survey of this region, obtained water from a 
depth of 1 1 10 feet, which had a specific gravity of 1.227, ^^^ 
which contained salts equal to more than a quarter of its 
weight. The analysis is instructive, showing, like all those 

^ Survey of Westei'n Palestine, Palestine Exploration Fwnd; "Geology," 
by E. Hull, p. 80. 

'-^ Quoted by Bischof, " Chemische und phys. Geologic,*' 2nd edit., Band i, 

p. 313- 



144 



OPEN-AIR STUDIES 



of the waters of this particular lake, a remarkable prepon- 
derance of magnesium chloride. Perhaps part of the sodium 
chloride has already been abstracted by the commencement 
of the process of deposition (see above, p. 142). The analysts 
found : — 



Magnesium chloride 
Sodium 
Calcium 
Potassium „ 
Calcium sulphate 
Potassium bromide 



» 



» 



14.590 

7.855 
3.108 

0.659 

0.070 

0.037 

26.319 



But there is every likelihood that the water of the Dead Sea 
becomes tampered with, as it were, by the volcanic springs 
which open into it. In any case, it is a very abnormal water, as 
we at present know it. M. Lartet,^ a French explorer, showed 
that the specific gravity at the surface was i .02 16, increasing to 
1.2533 at the bottom, with as much as 27.8 per cent, of salts. 
Should the Dead Sea finally evaporate altogether, a limited 
alluvial plain would be produced at the bottom, singularly 
placed some 1500 feet below the level of the Mediterranean. 
If we are here dealing, as in Utah, with a lake of fresh 
water slowly concentrated, in other areas we have similar 
phenomena produced by the drying up of portions of the sea. 
The plains around the Caspian were originally the floor of 
a sea extending northwards and westwards, at a time when 
probably the Bosporus was not yet opened. The Black Sea 
and the Sea of Azov then communicated with the Arctic 
Ocean, by way of the Caspian steppes and the Sea of Aral. 
Marine shells are found in the plains at present intervening, 
and the animals still living in the saline Aral and Caspian 
waters show an original connexion of these inland seas, both 
with one another and with the Mediterranean region. Slight 
earth-movements have raised a barrier which crossed the old 
line of communication ; even now a rise of 84 feet in the 
waters of the Caspian would connect it with the Sea of Azov ; 
by an increase of 242 feet it would reach the Sea of Aral ; and 
a further rise of 62 feet would cause this great sea to drain out 
by the Obi route into the Arctic Ocean.^ But no such results 

1 ** Voyage d'exploration II la Mer Morte," tome iii, p. 278. 

2 See W. B. Carpenter, article " Caspian Sea," Encyclopcedia BrUannica, 
9th edit., vol. V. 



ACROSS THE PLAINS 1 45 

are now obtainable, without a depression of the Aral region, 
or the elevation of a whole new continental ridge to attract 
the waters from the west. Mere filling up of the basin, as 
above suggested, might serve to connect the Black Sea and 
the Caspian ; but after that, to include the Sea of Aral, we 
must raise the level of the Mediterranean waters also, and 
hence of the Atlantic Ocean. 

It can be shown that the plains around the Caspian 
result from the diminution of the waters, for old shore-lines 
occur some seventy feet above the present surface ; and the 
shrinking of the older lake must have been rapid, seeing 
how slightly denudation has laid hold of the region between 
the upper terrace and the present one. The great changes 
in physical geography which cut up the former north-east 
sea and drained the Black Sea basin into the Mediterranean 
may actually have occurred since man appeared upon the 
earth. The great Danube itself may thus, almost in historic 
times, have sent its waters to the Arctic Seas. 

The present Caspian is, however, not necessarily a relic 
of the north-east sea. It may have arisen from a refilling of 
the old marine depression with ordinary river-water. It is 
certainly for the most part far less salt than ocean-water, 
and even than the enclosed Black Sea. But much of the 
salt is being withdrawn by deposition in certain areas of 
extreme evaporation, such as the highly saline Bay of Kara- 
boghaz ; into this a current constantly runs to maintain the 
level of its surface. 

The Desert of the Great Sahara is in parts a plain in 
which wind-action has full scope. It has often been said 
that its present surface was an old sea-bottom, like much of 
the country round the Caspian ; but recent enquiries have 
thrown doubt on this,^ and the plain as we know it may be . 
ascribed to wind acting in a region practically devoid of rain. 
Doubtless the old basin, an area of depression, was there 
ready formed at the time when the climate became dry and 
when vegetation began to disappear ; then the soils that had 
already accumulated were laid hold of by the prevalent north- 
east winds, and were carried into the air as clouds of dust. 
Much of the finer material may have disappeared, having 
gone to form loss elsewhere ; the sandy residue, with nume- 
rous coarser and pebbly banks, remains to form the desert 

* See De Lapparent, "Traits de Geologic," 3me ^it., p. 1393. 

E 



146 OPEN-AIR STUDIES 

floor; The sand-grains, rubbing constantly on one another, 
become cleaned and polished, to a degree unknown among 
river or sea sands ; larger pieces of rock become scored into 
and pitted by the friction of these particles against them ; 
and the wind also carries the sand in powerful blasts against 
the barren hills, and sculptures them into slabs and pinnacles 
and all manner of fantastic forms. The sand lays hold of 
natural lines of weakness, such as joints or bedding-planes, 
and excavates the rock along them; hence the horizontal 
stratification of some desert-cliffs becomes emphasised in a 
striking manner. The Sahara varies considerably in height 
above the sea, including several plateaus of 20(X) to 5000 
feet ; some parts are swept bare down to the bed-rock, which 
becomes polished by the passage of sand over it, while others 
show saline traces of former lakes. Sand-dunes 300 feet 
high have been formed in those areas in which the trans- 
ported material has taken refuge ; and smaller conical heaps, 
prolonged into crescents by the wind-eddies, are a common 
feature of the landscape. On the east of the Sahara, the 
sands of the Libyan Desert travel before westerly winds 
towards Egypt, which they literally invade, burying its tombs 
and templea The plain grows steadily in this direction ; in 
fact, we see here the delta of one of the broad currents of 
the air. 

Now we have probably learned enough, in running in fancy 
over all these regions, to convince us that plains have a genuine 
interest of their own. We may be living for years in an 
absolutely level country before it will yield up all its secrets ; 
and then we shall probably find that the enormous landscape, 
in which the sky plays so large a part, in itself reflects the 
history of the plain. Width and space, whether of wind or 
water, are the first necessities. Climates may have changed ; 
the sun may now look down through cloud-drifts where 
once it ruled in splendour; rich grass may have spread 
across the worn-down and scattered desert-dunes ; gleaming 
patches of salt may alone represent the blue waters of some 
inland sea ; but the sense of space is still with us, and the 
region is stUl a playground for every wind that blows. Even 
the mirage, by which the desert seems converted into a sheet 
of water, may be a faithful picture of the past; and the 
turning up of a common cockle-shell under the foot of the 
traveller may arouse trains of thought that will be a recom- 



ACROSS THE PLAINS 147 

pense for many weary days. But there — we have wandered 
far from our own familiar fenland. The moon is rising over 
the long chalk ranges, and the short grass gleams as if 
already touched with hoar-frost ; behind us the soft sheets 
of mist are stealing across the hollows of the fen. In an 
hour or so the express will carry us to London ; and there 
will still be time to catch the boat at Dover. 



CHAPTER VI 

DEAD VOLCANOES 

Our course now lies through central France, for we are 
bound on a perfectly new errand ; and the first landscape 
that we will consider is the view from Thiers, in the Depart- 
ment of the Puy de Dome. 

We arrive at the town from the east through a little 
granite ravine, where the road and the railway wind along 
the cliffs, the latter disappearing and reappearing among 
the rocks in true mountain-fashion. Then suddenly we are 
close to the roof-tops of the houses, which are piled on the 
steep descent to the valleys of the Dore and AUier. 

Over against us, five-and-twenty miles away, rises the 
long granite plateau beyond Clermont-Ferrand; and upon 
this is set the range of hills that we have come thus far to 
see. The steep -sided round -topped mass, conspicuously 
higher than the rest, is the famous Puy de Dome, 1463 
metres (4800 feet) above the sea. North and south of it 
a number of hummocky isolated hills form a broken band 
on the horizon. The great plateau is about 3000 feet above 
the sea, and many of the summits rise for another lOOO 
feet above it. 

This distant range is the ** Chain of the Puys," or the 
"Monts Dome," which have given such geological interest 
to the old province of Auvergne. The name puy is locally 
applied to any elevated mass short of a true mountain-peak. 
Even at this distance, the double character of the opposite 
wall of the valley can be discerned — the ancient plateau, 
part of the very core of France, and the row of puys 
placed disconnectedly upon it. 

We descend into the wide valley, cross the Dore at the 
foot of the terraced streets of Thiers, and the Allier also 
under the cliff of Pont du Ch§<teau. The roads are now 
made of the black rock known as basalt, masses of which 

we shall soon meet with on our way up to the granite 

148 



DEAD VOLCANOES 149 

plateau. Two miles on this side of Clermont, we pass an odd 
flat-topped little cone, quite diflferent from the other surface- 
features of the valley, and resembling the puys that now 
draw near above us.^ 

To understand a country such as this, it is well to make 
a preliminary survey from a height. We shall do well to 
leave the fine mass of the Puy de D6me till later, and to go 
up the winding road to one of the northern hills, the Puy 
de Pariou. The roadside-cuttings show us compact dark 
rocks, some of which have little hollows like bubbles in 
them. Occasionally we see the pale brown granite, which 
forms the foundation for the hills. 

We are now on the bleak and open plateau, with the 
enormous valley again below us, stretching northward to 
join the Loire. The ground is covered with heather and 
dry peaty soil, and beech-woods cluster thickly round the 
bases of many of the hills. Short wind-swept grass clothes 
the Pariou, and climbs the steep slopes towards the Puy 
de Dome ; and loose patches appear on most of these hills, 
where the rock seems too crumbling to allow the vegetation 
to lay hold. 

The beautiful curving outline of the Puy de Pariou 
attracts us even at a distance. The slopes lead up to a 
wide crest, which sinks again slightly iii the middle ; and 
on the north an outer rampart, like an artificial earthwork, 
follows the curve of the hillside. A very little inspection 
will show us that the whole hill is circular in plan, and that 
its summit-ridge forms a complete ring. 

It is a fairly steep climb after all, for the angle of 
the slope on the west is as much as 27°,^ and slips of the 
loose material seem common. We will examine the porous 
substance of the mountain later, when we have grasped 
the general structure. Above one of its broad bare regions, 
the crest is a little higher than elsewhere, rising some 750 
feet above the plateau ; when we reach it, we find ourselves 
on the edge of a great circular depression ; the ground, in 
fact, falls inwards towards the centre of the hill at a 

^ For a detailed description of this region and of its rocks, see G. P. 
Scrope, " The Geology and Extinct Volcanoes of Central France," 2nd 
edit, 1858, and A. von Lasaulx, " Etudes pdtrographiques sur les Roches 
volcaniques de I'Auvergne," 1875, translated from the German by F. 
Gonnard. 

2 Measured from a photograph by Mr. G. W. Butler, F.G. S. 



ISO OPEN-AIR STUDIES 

still steeper angle than it does towards the outer plateau 
(Plate V). 

This is altogether unreasonable, and contrary to the 
custom of ordinary hills. The cup-shaped hollow before 
us is 300 feet (93 metres) deep, and about three times as 
much across ; and its rim is often only five feet wide, and 
in places is almost sharp, requiring careful walking as we 
trace out its circumference, a stroll of more than half-a- 
mile. Prom this crest of vantage we look over other lesser 
puys, and perceive how this circular basin-shaped form is 
really typical of the district. The Puy des Goules, in 
particular, quite near us, has a perfect ring-shaped summit, 
broken only by a little clump of bushes on one side. 

Beyond the Puy des Goules is a round-topped pudding- 
like mass, which we must investigate separately. To its 
left is a stretch of woodland, and then the Puy de Chau- 
mont rises, with the same fascinating outline, its flanks 
slightly concave, as is so common in this group of hills. 
On its left is the steep Puy Chopine, a craggy mass 
defended by a rampart, like the half of a broad ring, 
the outer sides of which are seamed with water-courses 
formed in times of rain. In the far north other ring-shaped 
mountains rise, and then the plateau drops on that side 
also into the plain. On our left is the fine cone of the 
Puy de C6me, higher than the point on which we stand ; 
and a rough broken country descends from it, largely 
covered with wood, to the western valley of Pontgibaud. 

If we now examine the materials that build up the Puy 
de Pariou, we may gain some clue as to the mode of origin 
of this extraordinary group of hills. The loose bare portion 
of the slope is made of little stones full of bubbles, light 
and cindery, of various shades of grey, all heaped together 
to build the ring-like ridge. Were we to probe elsewhere 
into the grassy sides, we should find this same slaggy 
sort of material ; its very looseness, causing the rain to soak 
into the mass so easily, is said to account for the slight hold 
that denudation has upon the mountain. 

One of the best spots for seeing how the puys are often 
perfectly fragmental, beneath their covering of grass or 
trees, is the hollow in the Petit Puy de D6me to south of 
us. Here we have cindery masses of all sizes, purple-grey 
and purple-brown ; and some of the larger ones are spherical. 



! 









SI 



DEAD VOLCANOES IS I 

with a compacter crust and an interior more full of bubbles. 
The exposed slope is here so loose that it is very difficult 
to ascend. 

Surely all that we have read about volcanoes will come 
vividly before us here. A volcano is a place where molten 
rock, called lava, issues from the ground. Explosions occur, 
and "cinders" and "ashes" are scattered freely round the 
vent. Occasionally the lava itself flows out as a slowly 
moving stream, invading the lower slopes of the country. 
The outbreak or m^wption commonly occurs from the summit 
of a mountain, the opening whence the cinders and lava 
issue being funnel-shaped and styled the crater. 

The study of volcanoes was not undertaken in detail until 
nearly the close of the last century ; and the relations be- 
tween the eruptions and the volcanic mountain were at first 
only dimly realised. There was a natural idea, which is 
still very common among popular writers and journalists, 
that flames and smoke were the prominent features of an 
eruption. As a matter of fact, such flames as occasionally 
occur result from the ignition of gases in the crater ; they 
are pale, and are invisible at any distance. Smoke, such 
as occurs during the burning of compounds of carbon, is 
entirely absent. The white-hot melted rock, thrown up 
into the air, resembles at night a column of fire ; while fine 
dust is produced, together with dense clouds of steam, the 
latter being emitted at every throb of the eruption; the 
mingled matter, floating above the volcano, naturally re- 
sembles smoke. An enthusiastic student, indeed, once stated 
in an exaniination-paper that " a volcano consists of flames 
of smoke," which was going even farther into reckless error 
than the ordinary writer in the newspapers. 

Perhaps the most surprising fact is that the steam is the 
motive-power of the eruption. Water permeates all rocks 
down to great depths in the earth's crust. Now it is per- 
fectly certain that the interior of the earth is hot, though 
we are not prepared to say how far any part of it is actually 
molten. Miners, and engineers engaged in tunneling, fre- 
quently suffer from the rise in temperature, which careful 
experiments show us amounts to i° F. for every 50 or 60 
feet of descent, or 1° C. for every 100 feet or thereabouts. 
We do not know from these experiments, made as they are 
in one mile out of the four thousand between us and the 



152 OPEN-AIR STUDIES 

centre of the earth, whether this rate of increase of tem- 
perature is constant ; but it is clear that very high tempera- 
tures do occur within a short distance of the surface. Quartz 
melts at 1430'' C.,^ which might be reached in twenty-eight 
miles ; while a large number of rock-forming silicates could 
be melted at a considerably less depth. Dr. Joly shows us, 
indeed, that **a preponderating number of mineral bodies 
possess melting-points ranging within the comparatively 
narrow limits of 9CX)° C. to ISCX)° C." 

But probably the great pressures brought to bear upon 
masses at such a depth would effectually prevent their 
melting, since the liquid product requires more space than 
the solid and crystalline representative. Certain portions of 
the crust, however, such as the lines of junction of continents 
and oceans, are in a state of movement and unrest, whereby 
pressure is increased at some points and relieved at others. 
Any important relief from pressure, such as would be afforded 
by the lifting of the outer layers of the crust to form a 
shallow dome, will allow some of the highly heated rocks 
below to pass into the liquid state. 

Now, water has already permeated these rocks, but has 
similarly been subjected to pressure, whereby it has been 
prevented from expanding into steam. When any relief 
from this high pressure occurs, the presence of water assists 
in rendering the rock fluid ; and the water, moreover, begins 
to expand on its own account and to bear the whole mass up 
into any fissure that may be at hand. Should any portion 
of such a fissure reach the surface, the molten rock is rapidly 
lifted to the outer air, the water now expanding into steam. 
The vapour thus produced may escape with explosive violence, 
blowing the lava into fragments and sending them spinning 
hundreds of feet into the air. Such flecks of melted rock, 
fluid at the moment of their ejection, become spherical or 
elongated as they move swiftly upwards; a compact and 
often glassy crust forms on their outer surface, and the steam 
still imprisoned by this rapid consolidation renders them full 
of vesicles within. Such masses, perhaps two, ten, or twenty 
feet in diameter, are called volcanic bombs. 

More often, the melted rock, the lava, rises in the vent 
provided for it, and its upper surface cools and becomes 

^ J. Joly, *'The Uses of the Meldometer," Proc. Roy, Irish Acad., 3rd 
ser., vol. ii, p. 39. 



DEAD VOLCANOES 153 

solid, although remaining still red-hot. The product is like 
a scum, which heaves, and sways, and becomes broken up, on 
the surface of the liquid mass below. It is full of cavities 
where the steam has blown its way out of the viscid material, 
or has raised it into bubbles while struggling to escape ; and 
every now and then this crust of solid lava becomes blown 
suddenly into the air by the steam which has been imprisoned 
below it in the vent. Thus red-hot stones come flying out, 
accompanied by a great burst of steam ; 'these stones fall 
around the mouth of the volcano, and are called scorise) 
from an Italian word meaning a frothy scum. When cold, 
they may be picked up, and are seen to be irregularly shaped 
and full of bubbles ; and hence any vesicular rock is said to 
be scoriaceous. The scoriae seldom reach us in exactly the 
form in which they were blown off from the lava-crust; 
they come out in such abundance that they strike against 
one another in the air, producing a strong hurtling sound, 
and thus they become broken into smaller and smaller frag- 
ments. The somewhat coarse deposits formed of scoriae, 
usually with finer matter acting as a groundwork and as a 
cement, are known as tuffs, a word coined from the Italian 
tufa or tufo. 

Pumice, which is so widely used for cleaning purposes, 
is merely a refined and glassy type of scoria. The molten 
rock has been expanded by a vast number of steam-vesicles, 
which have become drawn out almost into tubular forms by 
the flow of the mass, as it rises and falls in the volcano and 
during its final ejection. If a piece of pumice is melted 
again, it shrinks into a black mass like bottle-glass. The 
white colour of pumice is merely due to the immense propor- 
tion of air-spaces that it contains ; light cannot pass through 
it, but becomes reflected again and again ; and the fibrous 
character of the mass gives it the lustre of spun silk. Pro- 
fessor James Dana found that some particles of pumice from 
the Sandwich Islands consisted of i per cent, by volume of 
glass and 99 per cent, of air-space. A freshly broken 
surface of pumice, examined with a lens, is an object of 
great delicacy and beauty. 

If two pieces of pumice, however small, are held one in 
each hand and are rubbed together, a very fine dust arises, 
which consists of tiny broken shreds of glass. This corre- 
sponds to the finer varieties of the material known as volcanic 



154 OPEN-AIR STUDIES 

dust or volcanic ash, which is produced by the friction of 
pumice fragments as they strike one another in the air. In 
all violent eruptions, this most delicate and glassy ash forms 
a large part of the heavy mammillated cloud that drifts 
away before the high currents of the atmosphere. A sifting 
process goes on, the bombs and coarser scoriae falling close 
around the vent, and many of them dropping back into 
it; the finer scorias lie somewhat farther away; while the 
minutely divided* ash is carried by the winds to immense dis- 
tances before it settles. The dust of Krakatoa, in the Straits 
of Sunda, erupted by the great explosion of August 26th, 
1883, travelled thus at least twice round the globe at a rate 
of seventy-six miles an hour. From their effects in producing 
a halo of a particular angular diameter round the sun, the 
particles of volcanic matter were calculated in this instance 
to be from .003 down to .001 millimetre in diameter.^ 

The illustration here selected (fig. 8) is reduced from 
one of the beautiful photographic plates accompanying Dr. 
Johnston-Lavis's work on "The South Italian Volcanoes."^ 
An explosion has just occurred in the crater of Vulcano, 
one of the Lipari Islands, and the dense cloud of steam 
and dust, at first r ashing vertically upwards, is now being 
carried along almost horizontally in the air. The last great 
eruption in this island occurred on August 3rd, 1888, when, 
among other striking manifestations, a block of lava thirty 
feet in diameter was thrown three-quarters of a mile from 
the crater, penetrating the volcanic soil to a depth of 
ten or eleven feet. Prior to January 26th, 1886, chemical 
works existed in the crater; the gaseous products rising 
through the fissures condense and even interact on one 
another, so as to cause a deposition of various salts of com- 
mercial value, which were collected at their point of origin. 
But on the date named these adventurous works were blown 
into the air, and the volcano has since been fairly active. 
In March 1890, for instance, it broke the windows of houses 
in Lipari by casting stones against them across a distance 
of four and a half miles.^ 



^ See Nature, vol. xxxiii (1886), p. 4834 review of work by Dr. Riggen- 
bach. 

2 Published by F. Furchheim, Naples. 

3 L. W. Fulcher, "Vulcano and Stromboli," Oeol. Mag., 1890, p. 347 ; 
and Johnston -Lavis, Nature, vol. xlii, p. 78. 



DEAD VOLCANOES 



155 



So mucli for the explosive stage of volcanic eruptioDS. 
But we all know that lava is often caused to well up com- 
paratively gently, to fill the crater, and finally to flow over 
as a lava-Btream. Or it may burst out at some fiBsnre 
opened in the lower part or in the fiank of a volcanic mountain, 
and may thence mn slowly bnt irresistibly down into the 
hollows of the country. Stream-cuts may in this way be 




Fiu. S.— Thb laLiMD OP Vm,CANO IS Ebuptiom, February n, i88g, 4. 
{Pliotographed by Proftttar U. J. JahntUm-LavU, F.G.S.) 



flUed up and obliterated, while cultivated lands are often 
rendered useless, until denudation and decomposition have 
formed a new soil from the surface of the consolidated flow. 
Such lava-streams give o£F steam and other gases while 
they are moving, and clearly it is the imprisoned water that 
has raised them to the mouth of the volcano and has forced 
them ont steadily in an oozy flow. Earth-pressures in the 
slowly moving crust may also urge on the viscid mass when 



156 OPEN-AIR STUDIES 

once an orifice has been found. Professor Judd^ regards 
the quantity of water present as of great importance in 
determining whether violent shattering action takes place, 
giving rise to volcanic dust, or whether, when it is in smaller 
amount, quieter upward propulsion occurs, such as gives rise 
to lava-streams.i In either case the products, having once 
been molten in the earth, are spoken of as igneous rocks. 

The temperature of lava-streams may reach 1200° C. or 
more ; but the mass is usually stiflE and pasty in its flow. 
In the crater of Kilauea, in Hawaii, there is a lava-lake of 
exceptional liquidity, a condition probably due to very high 
temperature. The proportion of water does not seem to be 
concerned in this case, as very little steam is given oflE from 
these Sandwich Island lavas. This lava-lake was recently ^ 
25CX) feet or so across, and the movements of its surface 
have again and again been compared to those of water. In 
an article in the Hawaiian Gazette of July 24th, 1894, there 
is a remarkable account of the changes accompanying a fall 
in the level of the lava. *' From about noon until eight in 
the evening," says the writer, " there was scarcely a moment 
when the crash of the falling banks was not going on. As 
the level of the lake sank, the greater and greater height 
of the banks caused a constantly increasing commotion in 
the lake as the banks struck the surface of the molten lava 
in their fall. A number of times a section of the bank 
from 200 to 500 feet long, 1 50 to 200 feet high, and 20 to 
30 feet thick, would split off from the adjoining rocks, and 
with a tremendous roar, amid a blinding cloud of steam and 
dust, fall with an appalling down-plunge into the boiling 
lake, causing ^reat waves to dash into the air, and a mighty 
' ground swell ' to sweep across the lake, dashing against 
the opposite cliffs like storm-waves upon a lee shore." 

Some of the masses which thus fell in from the sides floated 
on the liquid lava, being probably scoriaceous, and thus 
distinctly lighter, despite their solid state. One huge block 
is described as " plunging out of sight beneath the lava. 
Within a few moments, however, a portion of it, approxi- 
mately 30 feet in diameter, rose to an elevation of from 5 
to 10 feet above the surface of the lake, the molten lava 
streaming from its surface, quickly cooling, and looking like 

^ Krakatua Rep. Roy. Soc. Cummittee, p. 46. 
2 See Natv/rCj vol. 1 (1894), p. 483. 



DEAD VOLCANOES I 57 

a great rose-coloured robe, changing to black." Many of us 
will be acquainted with various popular accounts of the jets 
of lava thrown up from this extraordinary lake, which re- 
semble fountains, and which are scattered by the wind into 
showers of tiny globes and threads of glass. 

In ordinary volcanoes the lava is, as we have said, far 
more viscid than at Kilauea. But its rise and fall within 
the crater may similarly eat away the crumbling banks, and 
at last a breach may be effected, the wall of the mountain 
may give way, and the lava-stream may thus begin to flow. 

There seems no reason, from what we have already said, 
why volcanoes should break out upon the summits of hills. 
Indeed, numerous cases are known where the base of the 
volcanic mountain has been the seat of explosive operations. 
But conical masses, with a crater at the top, are certainly 
typical of volcanic action ; and they are, in fact, built up by 
the products of that action. 

The bombs and scoriae which fall around the vent do so in 
a fairly regular ring. On the inner side this heaped-up and 
increasing ridge slopes inward towards the vent, and newly 
added fragments are constantly slipping down and are 
ejected a second time, or are melted up in the central lava- 
column. On the outer side there is also a slope, somewhat 
more gentle, steep at the upper part, and then descending 
in a long and usually concave curve to the ground through 
which the volcano broke. These sweeping concave slopes 
are among the most beautiful forms to be found in any 
landscape. The rain spreads the finer ash at the base of 
the pile still farther from the centre, while the steeper upper 
rim is constructed of coarse scoriae. The rougher and the 
coarser these materials are, the steeper will be the slope, up 
to perhaps as much as 40°. Irregular heaps of still greater 
angle may be locally formed, by materials falling on one 
another in a state of partial fusion.^ 

This ridge of double slope, encircling the centre of erup- 
tion, is the simplest type of volcanic mountain. From a 
low ring it develops into a lofty cone, on which vegetation 
begins to climb. The scoriae suffer from atmospheric attack, 
and soils are formed for grass and even for trees, which cling 
to the somewhat treacherous slope. In some places lava- 
cones are formed, far less steep in outline, by the continual 

^ See J. W. Judd, "Volcanoes," p. 153. 



158 OPEN-AIR STUDIES 

overflow of the molten rock, now on one side, now upon 
another. In the case of the recent overflow of the lava-lake 
in the crater-floor of Kilauea, the material washed across the 
rim on all sides and rapidly made raised banks around the 
lava-basin. When the lava sank again, as above described, 
it was these banks that gave way with such magnificent and 
spectacular effect. 

Ordinarily, the crater-ring, the growing volcanic moun- 
tain, will be formed by a variety of actions, and lava-flows 
will roll across the ashes here and there, compressing and con- 
solidating them, to be in turn covered by loose scoriae. The 
prevalent winds may cause a heaping up of the fragmental 
materials on one side rather than on the other, and the crater- 
edge will become irregularly raised. The whole mass will 
form a volcanic COne ; the mountain is, in fact, the result of 
the volcano, though it is in no way necessary to its origin. 

The accumulated mass is, in the end, an obstacle to con- 
tinued activity. It may become so vast that the steam- 
pressure or earth-pressures below can no longer force the 
lava to the summit of the elongating pipe. Consequently 
outbreaks may occur upon the flanks; the cone may be 
cracked by the final explosion of long-imprisoned gases ; and 
sheets of lava may be forced into the fissures, consolidating 
there in wall-like masses and helping again to strengthen the 
whole mountain. 

These sheets (fig. 10), crossing the bedding of the rocks 
on which the volcano has been piled, and also that of the 
ashes and the lavas of the cone, are called dykes, from the 
fact that they weather out, after the volcanic action has died 
away, as approximately vertical wall-like masses. They give 
off little ramifying sheets and threads into the surrounding 
rocks, and these less regular offshoots are known as volcanic 
veins. Often the lava finds its way along the stratification- 
planes of the previously formed rocks ; we know how easy 
it is to slip even a thin and yielding sheet of cartridge-paper 
into its place amid a pile of others which it seems quite diffi- 
cult to lift. Earth-movements may assist this intrusive pro- 
^j|g, by slightly arching the strata away from one another ; 
^^^^K the lava may flow on underground for miles along the 
^ ^^ of weakness. Such masses are called intrusive sheets ; 
F V^'^) ^s ^* were, dykes which do not cross the bedding ; 

ftooner or later, as we trace them out along a denuded 



DEAD VOLCANOES I 59 

surface, we shall find them behaving as true dykeB, either 
where they have split into two or more sheets, or where they 
join up with the main line of fissure leading to the igneons 
levels. 

Where the molten rock of a dyke reaches the snrface, ita 
included water will rapidly throw up a aerieB of lava-cones 
or ash-cones, which are thus arranged along the line of 
fissnre. Or the lava may break out at one point of weak- 
ness only, and single subordinate cones will thus arise on 
the flanks of the greater volcanic mountain. 

A good example of the linear arrangement of cones 




Fio. 9.— SMiLL Comes THEtnwn cp os Etha, Ebbptioh of 189a, 
{Frum a photograph, ) 

occurred on Etna in 1892, where fonr craters were con- 
structed along a fissure which had already opened actively in 
1886 and 1883 • (fig. 9). These new hills have been named 
the Monti Silvestri. Monte Gemmellaro, erected also on the 
flank of Etna, and [500 metres above the sea, was formed as 
a bold detached cone in 1 886. Sixty-six million cubic metres 
of BCoriEe are calculated to have been piled aroand its vent, 
forming a new hill I40 m. (459 feet) in height; and the 
whole of this was built up by the explosions of twelve 

' G. Platania, in Nature, vol. ilvi (1893)1 p- 545- 



l6o OPEN-AIR STUDIES 

days, the mass thus growing in height about nineteen inches 
in an hour. 

Thus mountains may be visibly constructed on the surface 
of the earth at a very rapid rate. Another well-known histo- 
rical case is that of Monte Nuovo, on the Bay of BaiaB, near 
Naples, a scoria-cone which was built in 1538 to a height of 
440 feet in two days, the greater part of the work being done 
in twenty-four hours. Monte Nuovo is 8000 feet in diameter 
at the base, and stands partly on the site of a village named 
Tripergola, and partly on that of the old Lucrine Lake. 

From these simple cases it does not require any stretch of 
imagination to see how huge complex volcanoes may be built 
up. Could we cut such a one in half (fig. 10), we should find 
the central pipe or neck, filled probably with a plug of con- 
solidated lava ; the beds of ash would slope upward from this 
on either side, following the lines of the crater- wall, and 
would then dip away from the neck in a somewhat gentler 
slope, parallel to the outer surface of the mountain. Hard 
ribs of lava, the dykes, would occur, crossing our section at 
various angles, some coming from far below the base of the 
volcano, others arising from the volcanic neck itself ; while 
many of these would be seen to have sent off intrusive sheets, 
penetrating between the ash-beds of the cone. Lava-flows 
would also occur, forming compact bands among the ashes, 
and extending to various distances, according to their original 
degree of fluidity. A number of minor or '* parasitic " cones, 
of similar or simpler structure, would appear rising upon the 
flanks of the main one and complicating its otherwise regular 
outline. 

The crater of a volcano is liable, as we have seen, to 
breaching by the pressure of the lava within it ; it is also 
frequently enlarged by the violent and explosive phases of 
volcanic action. The whole upper portion of the cone may 
become blown away, perhaps in a few hours, and a wide 
crater-ring will be left, the central hollow of which is due to 
this vehement excavation. Subsequent milder action will 
build up a new cone in the centre of this area ; its sides will 
in time unite with those of the older mountain ; and thus the 
former dignity of the mass will be restored. 

Vesuvius itself is a comparatively recent cone raised in the 
shattered crater of Monte Somma. At present every erup- 
tion tends towards bringing the surface of Vesuvius nearer to 



DEAD VOLCANOES l6t 

the earlier crater-wall, until a handsome and uniform moun- 
tain will again be constructed, A volcano may, however, 
occasionally go too far, and may leave scarcely a wrack behind 
to tell the long history of its laborious up-piling. Kra- 
katoa had been already injnred by violent explosions which 
took place in prehistoric times, and showed traces of a crater 
of excavation some three or four miles in diameter,' It had 
began to fill up this hollow by the construction of several 
new cones, one of which, on the edge of the crater, rose to 
2623 feet above the sea. Between May 1680 and May 1883 
the volcano seems to have been dormant ; bnt the ernption of 
ash in the latter year culminated in the terrific explosions of 




August 26th and 27th. On these days two-thirds of the 
island of Krakatoa, and the whole smaller island of Polish 
Hat, were blown into the air, 1 8 cubic kilometres of rock, or 
4J cubic miles, being thus suddenly removed; and a hollow 
descending 1000 feet below the sea was. formed on the site 
of land which a day or two before rose from 300to 1400 feet 
above it. 

Those sensation-loving persons who are apt to chai^ 
Nature with being far too ^ow in her operations wQl surely 
find some comfort in a catastrophe of such startling mf^ni- 
tude. The rapid construction of volcanic mountains, on the 

^ J. W. Judd, " Krakstoa Report, Roy. Soc. Committee," p. 7, 



1 62 OPEN-AIR STUDIES 

other hand, explains those tales of old travellers and sea 
captains about "islands that have risen from the sea." Vol- 
canoes break out on the sea-floor as well as on the land ; 
there being no true "burning" about them, no true com- 
bustion, a supply of air is unnecessary for their activity. 
Hence a cone may be built up towards the sea-level, and 
may ultimately overtop it, forming a steaming volcanic 
island. Often such loosely piled masses have been washed 
away again by the waves, as was the case with Graham's 
Isle, which was formed between Sicily and Pantelleria in 
1 83 1. This island appeared on June i8th and vanished on 
December 28th, having at one time a well-formed and active 
crater. It represented the summit of a cone at least 240 
metres (787 feet) above the floor of the Mediterranean. 
After being cut down by the sea, it manifested itself again 
in 1863, after thirty-two years of quiescence, and rose to 
about 70 metres above sea-level ; but this attempt at 
island-making was also unsuccessful. In October 1891 
another submarine eruption occurred in this same restless 
area, the floating bank of black scoriaD formed above the 
eruptive centre being for a short time so dense as to be 
mistaken for an island (fig. ii). The volcanic bombs that 
rose freely to the surface burst there by the pressure of the 
gases inside them, and some actually ran hissing over the 
water, discharging steam.^ The scoria-shoal broke up and 
drifted away at the end of October ; but it is clear that the 
cone, which still lay far beneath it, may at any time resume 
its growth. 

A volcano is said to have undergone extinction when all 
sign of activity, in the form of upwelling of lava in the neck, 
has long ceased, and when it seems to have been given over 
as a prey to denudation. But volcanoes may, as we have 
seen, remain dormant for centuries ; and extinction is never 
abrupt, it is a very gradual process, broken at times by a 
startling return of the energies that seemed steadily flagging. 
Among the signs of waning activity, the prevalence of hot 
springs may be noted. In an earlier condition, steam-jets, 
looking at a distance like the cloud-columns of a true erup- 
tion, may occur freely from any rift in the crater-floor ; and 
other gases, such as Hydrochloric acid, Sulphur dioxide, and 
Sulphuretted hydrogen, rise in a highly heated state, the 

^ G. W. Butler, Nature, vol. xlv, pp. 154 and 584. 



DEAD VOLCANOES 163 

latter often decomposing as it bnrijs and depositing sulphur 
round the vent. These gases are given off during, as well 
as after, the ernptive period, and rise, with the Bteam, from 
the hot lava-flows themselves. But in time the temperatnre 
is insufficient to maintain these steam-jets or fnmaroleB, and 
hot BpringS take their place, the waters of which are charged 
with salts in solution — mostly carbonates and sulphates of 
sodium, magnesium aud iron — and with gases, the chief 
of which is carbon dioxide. It is this gas which gives bo 
bubbling and sparkling a character to the ordinary mineral 
WfUers placed npon our tables. The dissolved salts, varying 




in different localities, give a medicinal value to many springs 
and fashionable health-resorts are established od the scene 
of ancient eruptions. Thus, close to the charming hollow of 
Franzensbad, on the fringe of the Bohemian forests, near the 
hotels and bath-honses and promenades, there is one of the 
neatest and freshest little volcanic cones, the Kammerbiihl, 
as a reminder of the origin of the springs. The form is not 
well retained, but a large quarry has been dug into the hill, 
providing a remarkable section of the layers of volcanic ash. 
The scoriffi are perfectly preserved, looking as if erupted 
yesterday ; and they lie scattered also in the soil around the 
vent, which is now cultivated most peacefully. A bold row 



1 64 OPEN-AIR STUDIES 

of fir-trees rnnning up the back of the cone still looks greatly 
out of place. In the well-marked beds of scoriae, there lie 
numerous flakes, baked and reddened, of the old granitic 
rocks which form the floor through which the eruption 
broke. 

To make things more complete, a dull grey lava-flow 
runs down one flank of the Kammerbiihl, showing another 
phase of the activity of the cone. The whole thing might 
easily have been constructed by the explosions of any twenty- 
four hours. 

Some mineral springs of volcanic origin are by this time 
fairly cold; but others have retained their heat in a most 
interesting degree. Some, like the explosive Geysers, are 
thrown up by outbursts of steam, occurring at regular in- 
tervals. The water acts like the lava-scum in the vent of a 
volcano, and the steam, forming and accumulating in the 
hotter regions at the base of the pipe, finally overpowers it 
and flings it in a foaming column into the air. A beautiful 
little European geyser is to be seen in the source of the 
Sprudel at Karlsbad, in west Bohemia, where the water is 
thrown up to a height of ten or twelve feet some thirty 
times a minute. Its temperature is 162° F., and it still forms 
a delightful spectacle, although tamed and hemmed in by a 
marble basin and an ornamental hall of iron columns. 

In our own islands we still have the famous springs of 
Bath, with a temperature of about 115° F. The salts in- 
cluded in their water amount to 168 grains per gallon, or 
as much as .204 per cent. 94 grains per gallon consist 
of calcium sulphate; sodium sulphate furnishes 23 grains, 
and magnesium and sodium chlorides each 15 grains per 
gallon. 

Thus we have very briefly glanced at the life-history of 
volcanoes, such as are at present active on the earth. We 
have marked their growth, the occasional accidents that 
impair their symmetry, and the features of their period of 
decay. We can now look at their products more in detail, 
so as to be able to recognise them in regions from which 
volcanic activity has for long ages happily disappeared. 

All known lavas, whether in the form of fine ash, or 
scoriae, or massive flows, are found by chemists to consist 
of silicates. Some contain 75 per cent, of silica, others as 
little as 35, the substances combined with this prevalent 



DEAD VOLCANOES 



16S 

oside being oxides of aluminiura, potassium, sodium, 
calcium, magnesium, and iron. We cannot say in what 
relations these various bodies exist when the whole is one 
molten mass within the volcano; but, on cooling, crystals 
of definite minerals begin to separate out. If cooled 
rapidly, as on the walls of many dykes, or by contact with 
the air, the lava forms a glass, varying between black bottle- 
glass and the duller glass of iron-slags, such as one may 
pick up near furnaces in the English Midlands. Tet this 
glass is never free from tiny beginnings of crystallisation. 
When sections of it are prepared for the microscope (p. 25), 
minute imperfect groupings of crystalline particles are 
seen, these embryonic ciystals being called crystallites. 

Most crystallites are rod-shaped, 

and they become a^;regated, in 
the harried process of develop- 
ment from the glass, into more 
or less regular tufts and bunches. 
Sometimes they manage to take 
np true crystallographic positions 
with regard to one another, a 
number building up what is 
styled a skeleton-erystal. Very 
often they cluster round some 
central body and arrange them- 
selves radially about it, so as to 
form a little sphere, built up of 
fibres all pointing inwards to- 
wards the centre. Such bodies, 
often 2 mm. to 1 cm. in diameter, 
and sometimes even reaching i 
metre, are known as spheruiites, and are very characteristic 
of glassy rocks. Where artificial glass has remained a long 
time at the bottom of the tank in which it is being made, 
and has been subject to various coolings and reheatings, 
spheruiites often develop, appearing as little white balls, 
with radial structure, in the midst of the pale green or 
black-green glass. 

The dra^^ng movements that go on while volcanic 
glass is cooling set up a fiuidai stTuciure in the mass ; the 
material is still in motion, and the crystallites and spheru- 
iites are carried along, often forming distinct bands. Part 




FiQ. 12.— HicBoscopio Sec- 
tion OP VOLOAMO OLA8S 

(KuYOLiTB - Obsidian) fboh 

IHE YBLLOWSTONB PaRK, 

United States, x la, ihow- 
lag gpherulitic, fluidal, aud 
blinded st 



1 66 



OPEN-AIR STUDIES 



of the natural glass from a lava-stream in Lipari thus 
consists of alternate layers of black glass and creamy white 
closely set spherulitic matter. Such rocks are said to have 
a handed structure. 

The best known volcanic glass is Obsidian (fig. 12), 
named after Obsidius, an antique Roman who is said to 
have brought it from Asia Minor. The ingredients are 
such as a professional glass -maker would employ (see 
Analyses I. and II.), with the exception of some 14 per 
cent, of alumina. When the proportion of silica in the 
molten lava is less than 65 per cent., the chances of the 
production of a glass are much reduced, crystallisation 
then setting in more rapidly and the whole mass becoming 
dull and stony. Occasionally glasses are formed, however, 
out of difficult combinations of oxides, as is seen by the 
third analysis given below. In this case very complete 
fusion and rapid cooling seem to have worked together to 
produce crusts of glass some 2 inches thick upon the 
surface of the Hawaiian lavas. But the glassy mass dealt 
with in the second analysis is from 100 to 160 feet thick, 
with a few spherulites an inch across in places, and a 
number of more typical small ones (see fig. 12). 



Analyses of Artificial and Natural Glass. 





L 


n. 


m. 




Biitish Plate- 


Obsidian, Ob- 


Avemge of | 




Glass, St Helen's. 


sidian Cliff, 


12 Hawaiian 1 




Analysed by 


Yellowstone Park, 


Glassy Lavas, 




Mayer and 


U.S.A. Analysed' 


analysed by 




Brazier. 


by Hague. 


Silvestri. 


Silica . . ... 


n-z^ 


74.70 


48.25 


Alumina . . 


trace 


13.72 


15-65 


Iron Oxides . 


0.91 


1.63 


16.59 


Lime .... 


5.31 


0.78 


8.40 


Magnesia 


• • • 


0.14 


3-70 


Soda .... 


13-06 


3.90 


3-62 


Potash .... 


3.01 


4.02 


1-57 


Other substances and 


) 






loss on ignition (water, 


... 


1.02 

1 


0.41 


carbon dioxide, &c.) 
Total . 


) 




98.19 


99.65 


99.91 



DEAD VOLCANOES 



167 



AlmoBt all lavas contaiu a little glass, which has not had 
time to become entirely converted into crystallites. But 
as the mass cools more slowly, steadily parting with its 
imprisoned water, crystallisation goes on, until the products 
are visible to the naked eye ; well-developed crystals are 
thus formed, instead of mere tufts and spherical groups 
of crystallites. In microscopic sections, these crystals of 
various silicates are seen fitting into one another, those 
of the last-formed minerals often enclosing the earlier ones 
(fig. 13), while here and there a little glass, dusty with 
crystallites, remains between 
the mesh of crystals " 

The larger crystals often 
seen in lavas, and even en- 
tangled m the silky fibres of 
pumice are btyiedporphynHt 
since the rocks known to the 
ancients as ' porphynes are 
thus stuck tnll of crystals 
which are more conspicuous 
than those of the compact 
groundwork of the rock 
Porphyntic crystals are seen 
on minute examination, to be 
cracked and broken, and are 
often eaten into by the glassy 
matter of the lava. In sections 
they even look like lumjra of 
sugar that have just begun 
to dissolve. Such crystals, 
often the most attractive objects in the rock, cannot have 
developed during the consolidation of the lava as we 
now know it, hut have been formed in an earlier stage 
of consolidation and crystallisation underground, where the 
greater pressure, slower cooling, and perhaps the presence 
of water, allowed of their production on a handsomer and 
coarser scale. Then, by relief from pressure, or by further 
heating, or by the introduction of additional water, which 
assisted the mass to become more fluid, the lava ceased 
for a time to consolidate, moved forward, and floated the 
crystals already formed up with it to the surface. Some were 
no doubt completely redi^olved ; and those that remained 




FlO 13 — MlCRoaCOPIC '-BOTIOK OF 

Lava (Basalt) prom TuBBftMOBY, 
Moll, x 25, 6howingaugite(a)en■ 
clo9iDg pUgiodase (p) and aliviiie 
{ol), A part of tlie glassj ground- 
work, full of minute duat-lilia orjs- 
talline particle), appears on the 



1 68 OPEN-AIR STUDIES 

show, as we have said, signs of having been vigorously 
attacked. 

Porphyritic crystals are often, however, the relics of 
other rock-masses which have been picked up and partly 
melted by the lava on its way, certain mineral constituents 
alone remaining. Thus some lavas have become studded 
with quartz-grains derived from beds of sandstone through 
which they have been erupted. 

In the lavas fairly rich in silica, the following minerals 
may separate out on cooling from the mixed ingredients of 
the molten mass: — Quartz, Orthoclase, Albite, Oligoclase, 
Biotite, Hornblende, Augite (commonly a variety rich in 
soda). In those rocks poorer in silica, we have typically 
Labradorite, Anorthite, Biotite, Hornblende, Rhombic and 
Monoclinic Pyroxene, Olivine, Magnetite. In the ordinary 
lava of Vesuvius, Leucite in part takes the place of the fel- 
spars which so commonly prevail in other lavas. Leucite 
contains the constituents of orthoclase, but the proportion 
of silica in it is far less. 

Thus lavas, when crystallisation has set in, are seen to 
consist of mineral silicates, with one or two common repre- 
sentatives of the oxides, such as quartz and magnetite. 
Carbonates, sulphates, sulphides, chlorides — indeed, few com- 
binations but silicates-could exist at such high tempera- 
tures ; and, as we have seen, the more volatile constituents 
of the earth's crust come out as gases during volcanic 
eruptions, and continue to do so long after the lava itself 
has sunk into the condition of a cold and solid rock. 

There are four broad types of lava that are most com- 
monly met with : — 

I. Rhyolite. — ITie chemical composition of this rock is 
well shown by the analysis of obsidian, a glassy form of it, 
given above. Its name, meaning "flow-stone," refers to 
the frequency with which flow-structure and banding are 
observable in it (fig. 12). It is usually a pale yellowish 
white or pink rock, being poor in iron ; and its composition 
causes glassy forms to be common, which are distingnished 
by their superior transparency in thin splinters and by their 
low specific gravity from glasses with a less amount of silica. 
In its "stony" form, when the groundwork is a crowded 
mass of crystallites, rhyolite has a specific gravity of 2.5 ; 
in its most glassy form, the obsidian-type, it is as low as 2.3. 



DEAD VOLCANOES 1 69 

The crystals most likely to develop distinctly in rhyolite 
are Quartz, Orthoclase, Biotite, and sometimes Pyroxene 
rich in soda. 

2. Trachyte. — In this lava only some 60 to 65 per cent, 
of silica is present, but potash is still an important consti- 
tuent. The name refers to the " rough " (Tpa')(y<s) texture of 
the rock, in distinction to the compactness of most basalts. 
The colour is usually white or grey ; its glassy forms re- 
semble those of rhyolite, but are of higher specific gravity, 
the obsidian-type being about 2.4. The "stony" type of 
the rock gives about 2.55. The groundwork is most often 
formed of a mesh of minute crystals of orthoclase, with 
soda-pyroxene, hornblende, or mica ; larger crystals of ortho- 
clase, transparent and glassy-looking in modern examples, 
are scattered abundantly through this ground. 

3. Andesite. — In these rocks the silica may amount to 
even 70 per cent., but is sometimes as low as 55 ; soda 
always predominates over potash, and lime is prominent 
in those varieties containing little silica. The essential 
difference from the rhyolites and trachytes is that in the 
andesites plagioclase (triclinic) felspars crystallise out in 
place of orthoclase. The name refers to the abundance of 
this type of lava in the Andes Mountains. At one end of 
the great Andesite series we have light-coloured and even 
glassy lavas, like trachytes in appearance; in these the 
silicates of magnesium and iron are not abundant, and albite 
and oligoclase felspars, and even quartz, may crystallise out. 
At the other end of the series we have dark grey and black 
rocks, resembling basalts ; the glassy types among these are 
rare, and almost dull, crystallisation setting in so easily during 
cooling. These andesites, with some 58 per cent, of silica, 
contain lime, magnesia, and iron oxides, in greater abundance 
than is the case with the trachytic type ; and consequently 
black augite and rhombic pyroxenes often crystallise out, 
while the iron oxides that are uncombined with silica form 
magnetite. The felspars, whether forming a mesh in the 
compact ground or developed porphyritically (p. 167), are 
likely to be labradorite rather than oligoclase. The specific 
gravity of andesites, when fairly crystalline, rises from 
2.65 in the types rich in silica to 2.9 in those allied to 
basalt. 

4. Basalt. — The Andesites and the Basalts are probably 



I/O OPEN-AIR STUDIES 

by far the commonest lavas on the face of the globe. The 
percentage of silica in basalt runs from about 40 to S 5 ; iron 
oxides and magnesia and lime may now make up one-third 
of the rock's weight, or 33 per cent., while in the rhy elites 
they often are below 4 per cent. Glassy types are very rare ; 
an analysis. No. III., has been given on p. 166, which will 
serve to show the composition of basalts in general. The 
name Basalt is an ancient one, and is claimed by Pliny as of 
Egyptian origin. 

The groundwork of the rock is dark grey or black, typi- 
cally compact, and breaking almost like flint in the most 
finely grained varieties. There is a minutely sparkling effect 
over any freshly broken surface, which is produced by the 
glancing of the little crystals, so abundantly formed through- 
out the ground. Olivine may occur in porphyiitic crystals, 
and the presence of this mineral furnishes, as Professor Judd 
urges, the best distinguishing feature between typical basalts 
and the andesites poor in silica. But often the olivine may 
be decomposed, or may be visible only on microscopic exa- 
mination (fig. 13). Labradorite and anorthite felspars are 
common as porphyritic constituents, and one of these always 
forms a great part of the groundwork, together with little 
granular augites. Sometimes, as shown in fig. 1 3, the augite 
forms round and encloses the tiny rods of felspar. Magnetite 
separates out freely. The large amount of iron present 
causes surfaces of the rock to decompose on weathering with 
a marked rusty brown colour ; while the silicates of iron and 
magnesia alter to serpentine and chlorite, and colour the 
interior of the mass a dull and variable green. Thus basalts 
often become quite soft and friable through the easy decom- 
position of their constituents. The specific gravity of typical 
fresh basalt is close on 2.9. 

To sum up, we may classify our lavas thus in a 
table : — 



DEAD VOLCANOES 



171 



1 

Name. 


Approximate 

Percentage of 

Silica. 


Minerals typically 

produced in 

slowly cooled varieties. 


Approximate 

Specific Gravity of 

more crystalline 

varieties. 

(See also Table on 

p. 206.) • 


1 

Bhyolite 


70 


Quartz, 
Orthoclase, and 
Soda-pyroxene. 


2.5 


Trachyte 


• 1 


Orthoclase and 

Soda-pyroxene 

(or Hornblende, 

or Biotite). 

Albite 

(or Oligoclase) and 

Soda-pyroxene 

(or Hornblende, 

or Biotite). 

Labradorite and 

Augite (or Rhombic 

Pyroxene) ; 

Magnetite. 


( 2.6 


Andesite 

(a) Type 
rich in 
silica. 

(b) Type 

1 poor in 
silica. 


1 • i 

55 \ 


2.7 

2.8 


Basalt 


50 

V 


Labradorite (or 

Anorthite), Augite, 

Olivine, and 

Magnetite. 


2.9 



All lavas are likely to have certain characters impressed 
upon them during consolidation, apart from the occurrence 
of more or less complete crystallisation. We already know 
that their upper surfaces may be scoriaceous, owing to the 
escape of steam and the formation of abundant bubbles. 
The cavities thus formed have smooth inner surfaces, and are 
often beautifully regular and elliptical, being, in fact, spheri- 
cal gas-bubbles which have been pulled out in one direction 
by the flow of the lava. Owing to the rolling over of the 
advancing front of the lava-stream, the scoriaceous upper 
layers become carried to the bottom of the flow; and the 
lava-stream moves on over them and thus becomes coated on 
both surfaces with broken bubbly material. These surfaces, 
being products of fairly rapid cooling, will be the most glassy 
portions of the flow ; and more and more completely crystal- 



172 OPEN-AIR STUDIES 

line material will be found, after consolidation, towards the 
interior of the stream. 

Another striking character is the columnar jointing' of 
lavas. The rock becomes reduced in volume by contraction 
on cooling, and also by the loss of its water in the form of 
steam. A fairly regular series of joints is consequently set 
up in it, and the most common result is that the rock splits 
into a number of six-sided columns. Similar columnar joint- 
ing can be seen where clay has been dried by the sun upon 
a beach, and also in the starch used for domestic purposes. 
Clearly the structure is due to mere contraction, and not to 
any process of crystallisation. 

Now, the upper layers, cooling from the highest down- 
wards, exposed as they are to variable air-currents, and giving 
off gases somewhat rapidly, split into a large number of less 
regular and smaller columns, lying in many different direc- 
tions ; or they may merely settle down finally as a compact 
and somewhat scoriaceous mass. But the bottom layers, 
cooling from the lowest upwards, take far more time over the 
operation ; and columns more than a foot across may arise by 
the process of ** starring " against the colder ground-surface, 
and may spread upwards, as the whole mass cools, into or 
beyond the centre of the lava-stream. The outcome of these 
two modes of cooling, meeting in the interior of the mass, is 
that a large lava-flow is divided into a compact or only feebly 
columnar upper portion, and a handsomely columnar lower 
portion, any natural sections that may be formed showing us 
this striking contrast of the two layers. The columns start- 
ing from the ground are perpendicular to that fixed surface 
of cooling, and have all the appearance of well-trimmed 
masonry. Cross-joints, curved upwards or downwards, divide 
these columns into blocks resembling the " drums " of ancient 
pillars. It is no wonder that primitive peoples saw in such 
a regular structure in the solid rock the work of giants who 
built causeways in this lordly fashion. Later observers may 
also be excused for regarding the columns as some form of 
gigantic crystal. 

At the island of Staffa, the sea has quarried away the 
easily detached lower columns of a lava-flow, and has ex- 
cavated caves, the compactor upper layer holding itself 
together and serving as a roof. At a distance one can 
hardly believe that rocks of such distinct structure are 



DEAD VOLCANOES 173 

merely the regularly and the irregularly cooled portions of 
the same flow. At the Giant's Causeway, on the north coast 
of County Antrim, the rougher surface of a fine flow has 
been removed by weathering, and the ends of the columns 
of the lower part form a seaward-stretching terrace of 
wonderfully regular structure. When we look down upon 
them (Plate VI), they seem to form a tessellated pavement, 
the curving cross-joints sometimes appearing as flattened 
domes, sometimes as shallow cups in which rain-water and 
sea-spray collect. 

Any fair-sized dyke will similarly show columnar struc- 
ture due to its contraction (Plate VII). But in this case 
the two surfaces, if in contact with the same kind of rock, 
are under the same conditions of cooling. Often we 
have a selvage of glass on each side, perhaps a mere film 
only discoverable by careful search; this outer portion is 
broken by a large number of small closely set joints, and 
is usually friable in consequence. Then comes a region of 
partial crystallisation, the rock being flinty and compact, 
with columns developed perpendicular to the surfaces of 
cooling. The central region is often completely crystalline, 
the columnar structure there being coarser. 

The columns in dykes thus start independently from 
opposite sides and meet along a central plane, which con- 
sequently becomes a source of weakness in the mass. 
Weathering action attacks this plane, and sometimes the 
dyke becomes decomposed from its core outwards, leaving 
a gully to mark its former position, instead of standing out 
like a solid wall. Intrusive sheets possess similar char- 
acters, only here the columns are formed perpendicular to 
the planes of bedding. 

Another form of contraction which is very common in 
lavas and intrusive masses is the tendency to produce 
spheroids, which often lie one within the other. In its 
common and coarse variety, this spheroidal structure gives 
us a number of pillow-like masses, fitting into one another, 
like so many loosely packed sacks of grain heaped casually 
together. In its more perfect form, the rock has contracted 
in a series of concentric shells, which are often emphasised 
by the brown stains produced through the infiltration of 
rain-water. The resulting globes can be pulled out of the 
mass and easily broken up into concentric fragments with 



174 OPEN-AIR STUDIES 

the hammer. Many basalts show this structure upon 
weathering; and in the island of Ponza, west of Naples, 
a greenish columnar obsidian occurs, the columns sub- 
dividing into globes 3 or 4 inches to 3 feet in diameter.^ 

Well-marked spheroidal structure occurs commonly in 
the interior of the columns produced by previous contrac- 
tion ; and the curved cross-joints already noticed at the 
Giant's Causeway and elsewhere are a manifestation of the 
same tendency. Ferlitic structure is a minute spheroidal 
structure occurring only in glassy rocks, ofjien in great per- 
fection. The rock becomes broken up by it into little 
pearl-like masses, formed of concentric coats like those of 
an onion, these globes being only about 2 mm. in diameter. 

Dykes and intrusive sheets naturally bake and alter the 
rocks on both sides of them ; but lava-streams can only 
affect the bed below them, and that merely in a slight 
degree. This fact is at times of service in determining 
whether some ancient volcanic mass is a flow or an intrusive 
sheet. If the former, it is of the age of the deposits in 
which it is found embedded ; if the latter, it may be of any 
age later than those deposits, and other evidence as to its 
exact period of formation must be looked for. A maximum 
age for an intrusive rock can often be arrived at by the 
discovery of pebbles worn from it lying in some neighbour- 
ing conglomerate. Clearly the rock was cold and denuded 
before this conglomerate was laid down. 

Now let us return to our high bleak plateau of Auvergne, 
armed with these ideas as to the characters of modern 
volcanic action. It was thus that MM. Guettard and 
Malesherbes approached the problem a century and a half 
ago ; and there is little diflSculty now in recognising the 
Puy de Pariou as the scoria-cone of an extinct volcano. On 
the north-west side, moreover, we have already noticed a 
distinct semicircular rampart, and this represents an older 
crater-ring on the ruins of which the Pariou has been thrown 
up. Eastward from this earlier crater, there stretches a 
rugged surface of grey rock, confused and broken, descend- 
ing over the steep edge of the plateau towards Clermont. 
This can be nothing else than a huge consolidated lava-flow, 
which has breached the older cone. 

^ G. P. Scrope, " Notice on the Geology of the Ponza Isles," Trans. Oed. 
Soe. London, ser. 2, vol. ii (1824), p. 205. 



DEAD VOLCANOES 175 

We can follow out the course of this magnificent mass 
of andesite, as it rolled at red-heat across the granite slopes ; 
we can see where it struck on a knoll at La Baraque, still 
looking, as Scrope says,^ like " a huge wave about to break 
over the seemingly insignificant obstacle." Here it split 
into two narrow flows, the velocity of which must have been 
considerable, as they hurried down the valleys already cut 
in the plateau-face. One of these tongues reached nearly 
to the site of Chamaliferes, the other to that of Nohanent, in 
each case a course of about 8 kilometres from the shattered 
cone of Pariou. Near Chamaliferes the end of the flow rises 
in a steep and rugged front ; and beneath it are the remains 
of a wood which it bore down upon and overwhelmed. 

Several quarries in this lava-flow have revealed its inner 
structure ; its upper and lower portions are distinctly scori- 
aceous, while the centre is only minutely so, and is, as we 
should have expected, of compacter texture. The northern 
branch, exposed in the Durtol quarries, is exceedingly com- 
pact and altogether darker in its colour.^ 

When we become accustomed to the features of this 
highland of Auvergne, we shall easily pick out the lava- 
flows with the eye, by their rugged surfaces of confused 
grey blocks, their scoriaceous texture, and the fact that 
they are often abandoned to a growth of wild underwood 
and forest. The Puy de Louchadifere, one of those whose 
tops we can just see beyond the Puy Chopine, will thus 
well repay a visit. The huge scoria-cone, 1300 feet above 
the plateau, is breached on the west by a flow of basalt, up 
which a track now wanders into the crater. But the moun- 
tain itself is piled upon earlier flows of andesite, which have 
become somewhat smoothed down, but which may be traced 
away into the hollow of Pontgibaud. Farther south, two 
flows, each one and a half miles wide, form rugged and 
tree-covered slopes descending from the Puy de Come ; the 
most northern branch of these, reaching Pontgibaud, has 
been there cut into by the river, the columnar structure of 
its basal layers being revealed. 

The most delightful of breached cones are a pair lying 
east of the quaint little hamlet of N^bouzat ; and we must 

1 '* Geology and Extinct Volcanos of Central France," p. 63. 
^ For a minute description of these rocks, see Von Lasaulx, "Roches 
vole, de I'Auvergne," pp. 55-72. 



176 



OPEN-AIR STUDIES 



climb the Puy de Vichatel or some neighbouring height to 
view them. The Piiy de Lassolaa and the Puy de la Vaohe 
then appear as two bare pink-brown scoria-cones, broken 
open completely on the south side, and giving out a flood of 
lava (fig. 14). The pnys beyond them are grass-covered, 
with the denuded rock of the Puy de Dome rising palely in 
the background ; and these red and loosely piled masses in 
front of us look as if they had been thrown up only a year 
or two ago. But the lava-flows, uniting on the plateau, are 
covered with characteristic woodland, in which the grey scori- 
aceous blocks of basalt stand up like the Mbris of a landslip. 
The course of the joint flow, with its offshoot to the left. 




Pia. 14.— Thb Put db Lassolas 



?:S?^ '?<■'?"" 



E ViCHATEL. 

FTi a tktUh bg Oit Avthor.) 



where it struck against the puy on which we stand, is clearly 
marked by the line dividing the wooded country from the 
fields. The tumbled mass flows away to onr right, where the 
high road has been cut through it, and falls some 600 feet 
into the valley of the Veyre (fig. 15). Here it has dammed 
up the river and formed the Lake of Aydat, a good kilometre 
in length, the water escaping round the foremost tongue 
of the lava. Another lake, now drained, was formed in a 
similar manner farther north. This is a good example of 
how the face of a landscape may be changed by a lava-flow, 
perhaps in the course of a few hours. 

Beneath this basaltic stream, which itself is three and a 



DEAD VOLCANOES 



half miles (5J km.) long, an earlier one appears, running 
down the narrow valley to St. Amand-Tallende, some five 
miles farther to the east. The Veyre has partly cat its 
channel in this flow, and at Ponteix wanders through its 



Ash 




Scale of Kilometres 



FiQ. 15,— Gboloqical Map, showibo Lava-Flowb descbmdiko from Pura 

IN AnVERONB. 

I From Sheet 166 of iKe Map of the Qtoloeioal Swvei/ of Frana. ) 



crevices ; but finally it found the rock too hard for it, and 
made its way along the northern edge, between the lava and 
the soft sediments of the plain. It is thus that these rugged 
masses are left standing out above the general level, and are 
perpetuated as feature of the landscape. 




178 OPEN-AIR STUDIES 

Within the breached craters of the Puys de Lassolas and 
de la Vache, the bedding-lines of the scoriae can be clearly 
seen. These barren little cones, fresh and brown and sharply 
rimmed, despite the great outpourings of lava, form the most 
effective volcanic picture of the whole chain of the Monts 
Dome. 

If we return north to the exquisitely regular scoria-cone 
of the Goules, we find that it is banked against a broad 
pudding-like dome of trachyte known as the Grand Sarcouy, 
a name believed to be derived from the fact that the Eomans 
quarried this pale rock for making sarcophagi, or stone coffins. 
This mass is shown above the Goules in our illustration 
(Plate V). The great Puy de Dome itself is probably another 
but steeper mass of the same kind, and so also is the peak of 
the Puy Chopine, which appears over its outer rampart on the 
left of the Puy des Goules. These singular rocks were pro- 
bably thrust up in an exceedingly pasty form, each through 
its volcanic vent, and became consolidated in huge domes 
upon the surface. The Sarcouy is certainly one of the 
oddest hills that it will be our lot to see ; and Mr. Scrope 
observed in certain of the caves in its interior a layer-like 
structure, apparently parallel to the surface of the mass. A 
similar structure appears in the brown trachytic mound of 
the Schlossberg, near Teplitz in Bohemia ; the surface of this 
hill is largely controlled by the flaking off of its concentric 
coats, the fragments lying freely in the woods upon the lower 
slopes. Professor Reyer,^ who investigated the mass, con- 
cluded that it also was a protruded dome, the successive coats 
naturally arising, as the new material from below welled up 
and stretched the older and still viscid layers which lay above. 
Professor Reyer has successfully imitated the Schlossberg and 
other domes by forcing up moist plaster-of-Paris through a 
hole in a board. 

Far more often, lava welling up, without being blown into 
scoriae by the escaping steam, forms round the vent a true 
and gently sloping lava-cone. An example of this is pro- 
bably to be found in the Puy de Charade, south of Roy at, 
where a circular area of basalt, with handsome porphyritic 
olivine, caps a granite knoll and flows away to the north-east. 
No sign of an actual crater is now visible. 

^ " Ueber die Tektonik der Vulcane von Boh men, " Jahrh. d, k. k. ged. 
RehsanataU, Band xxix (1879), p. 464. 



DEAD VOLCANOES 1/9 

The volcanic craters of the Monts Dome have been ex- 
tinct, humanly speaking, for a long time ; but man himself 
was probably in the countiy when the later scoria-cones were 
exploding in the height of their activity. The oldest vol- 
canoes of the central plateau of France belong to what is 
called the Pliocene period, which immediately preceded that 
in which we still are living ; and at that time the ground on 
each side of the granite platform had only recently been 
raised above the sea. The volcanoes, in fact, were, as so 
often happens, the natural accompaniments of movement in 
the crust of the earth. 

The recency of their extinction is shown by the abun- 
dance of mineral springs which still flow out at the base of 
the plateau, making Eoyat, La Bourboule, and Mont Dore 
famous among health-resorts. Here and there the waters 
have filled the craters, forming characteristic crater-lakes. 
It is a pretty sight to stand upon the col under the Pic de 
Sancy near Mont Dore, and to look over the rolling country 
to the south, with its fold on fold of basalt hills» In this high 
volcanic plateau lie several circular lake-basins, notably Lake 
Pavin and Lake Chauvet near at hand. Both these are 
encircled with crater-rings, and the loose shore of scoriaa de- 
scends with strange steepness into the calm and sheltered 
water. Fir-trees have crept over the shallow rim of the vol- 
cano, and have grown about the central lake. Everything 
to-day thus speaks of quiet and extinction. 

The earliest volcanic masses, those of Mont Dore and 
the romantic highland of the Cantal, have already been cut 
deeply into by denudation. At the very gate of Mont Dore, 
with the beautiful cones of the Monts D6me still fresh in our 
memory, we pass the steep valley leading down to Eochefort, 
and see disconnected relics of old lava-flows left as mere 
patches on either side. The trachytic crags of the Eoche 
Sanadoire and the Tuiliere have probably been carved but 
of the same great mass ; they rise up like huge gate-posts 
flanking the valley, and are most perfectly columnar, the 
structure repeating itself in tiers at various angles. White 
taluses stream down at the feet of these two crags, and no 
cone or crater remains to show whence the trachyte flowed. 
The walls of the long combe of Mont Dore are marked with 
layers of white trachytic tuff and dark little cliffs of andesite ; 
the forms of the landscape no longer depend upon volcanic 




l80 OPEN-AIR STUDIES 

accnmnlation, but peaks and hollows are cat regardlessly 
throngh the depK)6its, and a complex moantain-mass has 
resalted, reminding one of central Wales. 

Again, in the soath, beyond the denuded volcano of Mont 
Dore, the country is set with mere relics of the former flows, 
such as the high crag of Apchon, one of the most beautifully 
columnar basalts in the country. The peak of the Puy Mary 
of Cantal (5861 feet) is carved out of both andesite and 
trachyte ; the scoria-cones have disappeared, and have left 
merely bands of tuffs, which are visible along the crags 
above the woodland. The crest of the mountain forms the 
centre for a radiating series of aretes, each spreading out- 
wards as the wall of some splendidly proportioned valley. 
At sunset the level light streams in from the Bordeaux plain, 
and fills all the western hollows with a golden haze ; the 
shadow of the Puy Mary climbs slowly across the valley of 
Aurillac, and the highland-pastures, and the little huts of 
the cheese-makers, die slowly away into the gloom. As the 
silence spreads, we hear the noise of torrents more clearly 
from the hollow far below ; the valley is almost choked with 
dibris, through which the water is busily cutting a ravine. 
Everywhere we have the grand air of a mountain given over 
to denudation. In time it will be difficult to trace even the 
worn-down centres from which these lavas of the Cantal 
were erupted. 

If in so short a space of geological time these volcanoes 
of the Pliocene period have lost all their characteristic out- 
lines, if the crater-rings have vanished and the lavas have 
become dissected into fragments, it is scarcely surprising 
that in our own islands we have nothing that we can point 
to as a cone. We have volcanic relics in plenty, but the 
atmosphere and the sea have long worked their will upon 
them. Serious tourists, proud of their attainments, will 
point out a small grassy hollow on the top of Staffa as the 
crater whence the lava flowed, regardless of the fact that the 
whole island is a mere remnant of a stream of basalt, resting 
regularly upon a bed of ash. Similarly the cirques of our 
higher mountains are annually pointed out as craters, particu- 
larly on the front of Cader Idris. In that instance they 
are, like the Cantal valleys, supremely indifferent to the 
original form of the volcano, while in a great number of 
cases there is no erupted matter in the neighbourhood of 




DVKE OF DOLERITE, 



Chalk and Basaltic Lavas, 

The upper putt it diiLinclly cotumUT. Tilni u (wt. 

I /■*•*.(«./*.■</*/ Mt- R. Wblch. 



DEAD VOLCANOES l8l 

these cliff-set hollows. The task of tracing out the history 
of one of our own volcanic areas is, however, always fasci- 
nating ; and the remarkable observations of Dr. Macculloch, 
Professor Judd, and Sir A. Geikie, in the Western Isles of 
Scotland have led a number of enthusiasts into the same 
attractive field. 

Without doubt, the most convenient region for the study 
of British volcanoes is the country around Belfast. The 
cinder-cones have been swept away by denudation, but the 
volcanic necks and dykes remain. Everywhere the greater 
heights of County Antrim are formed by plateaus of basaltic 
lavas ; and the contrasts of form and colour are as clear as 
a diagram in a lecture-room. 

The coast of this fine county is strange, but always 
beautiful. Long slopes of red clays and sandstones lead 
down in places to the sea ; above them here and there blue- 
black clays can be seen in the road- side sections; higher 
still, the ground rises steeply, and is quarried away, showing 
bands of white limestone, the chalk of Antrim. The capping 
of the whole is a bold dark cliff of basalt, formed of tier on 
tier of lava-flows, with occasional ash-beds, its jutting spurs 
and pinnacles weathering out in tints of ruddy brown. 
Beyond Lanae, the white limestone, the chalk, comes down 
to the shore, and cliffs have been cut in it like those of south- 
east England ; while the volcanic layers form the upper half 
of the wall, bare and brown and crumbling. The waters from 
the high basalt moorland flow down in the clearest streamlets 
into gullies carved out of the chalk ; and the black volcanic 
pebbles lie picturesquely in these snow-white hollows. Every 
now and then a dyke is seen (Plate VII) filling some old 
fissure, formed in the time of disturbance and activity, and 
cutting both the bedding of the limestone and the oldest 
lava-flows above. 

The interior of the county, as well as the east of County 
Derry, is formed of gently swelling basalt plateaus, every 
older feature being concealed by the union of the flows. 
Heather grows freely ^on these uplands, and peat is cut by 
the peasants in the broad levels of the bogs. It is a strange 
and often desolate landscape, nearly devoid of trees, and 
covered in winter with undisturbed sheets of snow. But, 
when we come to the plateau-edge, the scenery is rich in 
its variety. After the long pull across the mountain from 



1 82 OPEX-ATR SrrDIES 

Coleraine. we drop steeply from the lavas to the allnYinm of 
the River Roe ; or we may come roand by the coast under 
gloomy cliffs of basalt, all the more impressive by contrast with 
the recent sand-banks of Loncrh Fovle. Awav. a^rain. on the 
east of Connty Antrim, in the hollow of Cnshendall. we see 
the plateaus dissected into a nnmber of bold moantain-spurs. 
The cliff of basalt runs round these, making a fine outline 
at its angles against the sky ; but the crests of the spurs are 
all of about one height, being formed of the broad rounded 
backs of the united lava-flows. Farther inland, the highest 
sheets of basalt, which have been denuded away from these 
lower ridges, form another great platform in this step-like 
country, reaching some 1800 feet above the sea. The glens 
that have been cut into them stretch down to the woodlands 
of Cushendall, and far older volcanic masses are exposed 
down there upon the shore itself. Near at hand, dominating 
the valley, the cone-shaped summit of Tieveragh rises, the 
solid neck of a volcano that has loner since been worn awav. 
In the south, across the bay, the chalk cliffs gleam under 
the dark coping of the basalt, and give us some clue as to 
the geol(^cal age of the eruptions. 

The volcanic character of such a country is unmistakable. 
If we merely climb the steep side of Cave Hill above Belfast, 
and wander along the curved front of the cliff, we shall find 
scoriaceous rocks in plenty, sometimes compact, uniform, 
and black, sometimes with a delicate groundwork in which 
the crystals are just visible to the naked eye. In many 
cases the steam-vesicles are partly or wholly filled up with 
white minerals ; these are hydrous silicates derived from the 
alteration of the felspars, and are occasionally accompanied 
by quartz, which was deposited during the same chemical 
changes. Often the cavity became lined at the outset with a 
green earthy layer, respiting from the attack of water ujwn 
the silicat^^ of mm and magnesia, compounds of these mate- 
rials being amrmg the earliest minerals to decay. Within 
this green layer, the nest of clear and colourless silicates 
has l^en ftmnHd. Such a structure is called amygdaloidal, 
from the (ireuk word for an almond, the rock looking like 
a dark cake ntnck full of little almonds. These secondary 
mmeraU in the steam-hollows often crystallise inwards in a 
delicate fibrous fashion, and their structures are well worth 
studying with a lens. 




Plats VIII.I 



\Fk»U[Ta^lJ if Mr. R. V 



DEAD VOLCANOES 1 83 

In the cliffs of the north, towards the Giant's Canseway, 
the double structure of the lava-streams is magnificently 
displayed (Plate VIII). Tier upon tier of black-brown 
rocks are exposed on the storm-swept headlands, columnar 
structure standing out superbly in almost every alternate 
layer. The layer above each zone of columns is the upper 
and more irregular portion of the stream; and here and 
there some massive flows have escaped columnar division 
altogether. We have already seen (p. 173) how the admir- 
ably perfect " Giant's Causeway " is merely the basal part of 
a lava-stream, which is found in its entirety in the terraces 
of the cliff above. Red bands sometimes occur between the 
lava-flows, and are especially striking on the volcanic coast 
of Skye. These represent the oxidised surfaces of decay 
formed in the interval between one lava-flow and the next. 
Soils were produced by atmospheric action, and vegetation 
at last rose upon the consolidated lava. Leaves and twigs 
were washed into the little pools that accumulated in the 
hollows, and crusts of red and brown iron oxide were de- 
posited in nodular masses upon their floors (see p. 142). In 
time all this was covered by another flow, and the nature of 
the leaves, thus remarkably preserved, has enabled geologists 
to fix the period at which these Irish volcanoes were in 
activity. 

Similar leaf-beds occur in the west of Mull, as thin layers 
amid the frowning cliffs of basalt, and show that the great 
volcanoes of the Hebrides were also pouring out their lavas 
at the same time as their rivals in County Antrim. Indeed, 
at that period, later than the deposition of the Chalk, there 
must have lain " underneath the area of Britain a reservoir 
or series of reservoirs of lava, the united extent of which 
must have exceeded 40,000 square miles." ^ 

Besides the andesites and basalts. County Antrim con- 
tains examples of almost every variety of rhyolite, and a 
whole broad hill north of the Tardree Mountain is coated 
with a lava-flow of obsidian, which is now breaking up into 
decaying boulders amid the peat-bogs. 

The formation of the lava-plateaus, here and elsewhere, 
is fairly easy to understand. The tendency of long-con- 
tinued eruptions is to fill up all the hollows of a country, 

^ A. Qeikie, ** The History of Volcanic Action during the Tertiary Period 
in the British Isles," Trans, lioy. Soc, Edinburgh^ vol xxxv, p. 72. 



I 84 OPEN-AIR STUDIES 

as we have seen in the case of the lavas of the Pny de Come 
and the Lonchadiere. The fluid basalt imitates, as it were, 
an alluvial flat, and on this level floor, perhaps a century 
later, another flow accumulates. This may not occupy the 
whole width of the valley, but a third one may come down 
and fill it up completely. Meanwhile, neighbouring valleys 
have been similarly choked, and at last the ridges between 
them are buried by lavas piled to so high a level that they 
have been able to override the barriers. A long succession 
of events like these covers the whole country with an almost 
uniform surface of lava, above which a few scoria-cones, 
breached by the flows or thrown up later, rise picturesquely 
and indicate the actual vents. 

These cones then become destroyed by denudation ; again 
and again they have arisen during the long history of the 
plateau, to be washed down into level tuff-beds and to be 
buried by eruptions from some other source. A stratifica- 
tion is thus established in the volcanic series, which imitates 
the horizontality of marine deposits. 

But, if we try to follow out one of the lava-streams 
over some long cliff-face, we shall find that it is not a 
broad sheet, flooding half a county from some continuous 
fissure in the crust, but that it terminates in a narrower 
edge on either side. The apparently uninterrupted stratum 
that attracts us at a distance is really built up of several 
flows ; ^ these have run down side by side, but at different 
periods, the one making good the deficiencies of the other, 
and the whole series conspiring to level up the surface of 
the land. 

The north-eastern counties of Ireland were formerly like 
those of south-east England, a country of rolling hills of 
chalk, with their upper slopes covered with short grass, 
and their hollows cumbered with flint-gravel, the product 
of their own decay. Through this upland, in what we call 
the Eocene period, the volcanic action broke ; here and 
there a huge cone arose, rapidly piled upon the scorched 
and shattered Downs ; but the ground, like that of Auvergne, 
yielded at several points at once, and flow after flow of 
andesite and basalt were poured forth from a number of 
small vents. The lower flanks of Etna at the present day 
show us somewhat similar features. 

* See A. Geikie, work above quoted, p. 80. 



DEAD VOLCANOES 185 

The abundance of dykes in County Antrim points to 
this multitude of vents. These dykes are difficult to trace 
inland, owing to the grass and the bogland of the plateaus ; 
but in quarries and along the shore they are conspicuous. 
Carrickfergus Castle, which rivals Caernarvon in its position 
as a stronghold of the sea, is built upon a weathered-out 
basaltic dyke, which is exposed for about a mile and runs 
out like a spur into the water. 

Scrabo Hill, an isolated relic in the north of County 
Down, is a marvellous dissection of one of these Eocene 
volcanoes. Great quarries have been opened in the pink- 
brown sandstones which form so large a portion of the 
hill ; and dark basaltic dykes can be seen running up across 
these artificial cliffs, and sending off sheet after sheet along 
the planes of bedding of the sediments. Nothing on the 
slopes of a modem volcano can be clearer than the sections 
thus revealed. The upper part of the hill is formed of 
sheets of lava, some of the dykes penetrating these also 
and reaching the present surface of the ground. 

Cammoney Hill, north of Belfast, contains the neck, 
conveniently quarried into, of another of the old scattered 
cones; this mass is oval in section, and about a third of 
a mile across. Naturally, this slowly cooled volcanic plug 
has became completely crystalline. At Carrick - a - rede, 
again, some miles east of the Causeway, there are extensive 
beds of volcanic tuft, and a well-marked neck, which is 
exposed by the cutting of the sea. This vent was about 
1000 feet in diameter, and is choked with "a coarse 
agglomerate, in which blocks and bombs of basalt, with 
pieces of chalk and flint, are stuck at all angles in a dull 
dirty-green granular tuff."^ Another centre of eruption, 
conspicuous for miles around Ballymena, is the grand mass 
of Slemish, rising like a huge fortress, girt with cliffs, 
above the long curves of the basalt plateau. It may once 
have been surrounded by a cone of ash and tuft, culminating 
1500 feet above the sea; but it now stands out as a de- 
nuded core, the one true mountain in the county. It is 
still suffering from attack, and the clouds gather first upon 
it when the moist wind blows from the great sea-inlets 
of the west. 

Pair Head itself (Plate IV), one of the noblest promon- 

^ Geikie, work above quoted, p. 105. 



I 86 OPEN-AIR STUDIES 

tones of onr islands, is an intrusive mass some 250 feet in 
thickness, banked up below by a tains of blocks as large as 
houses, and rising above in a sheer black wall of strikingly 
columnar structure. Its rugged back is worn out into hol- 
lows in which little lakes have gathered ; and from its summit 
of 636 feet we see in the south the long dark plateau-edge, 
resting on high exposures of the buried Downs of Antrim. 

The formation of plateaus by accumulated lava-streams 
is seen even better in the desolate north of Skye, where 
the landscape is one long series of platforms, piled upon one 
another, with brown columnar steps between them. Bog- 
myrtle, and Cotton-grass, and the pale stars of the Grass 
of Parnassus, grow upon these bleak wet uplands ; while 
the air is always tinged with soft grey rain, and the smell 
of sodden oat-fields rises from the crofts along the hollows. 
In the shallow valleys the view is cut off by the basalt 
tables on either side ; and it may be a walk of miles across 
the yielding bog before we can attain some watershed and 
look out on the Atlantic and the isles. It is hard at first 
to compare these brown-green watery uplands with the 
cleanly outlined and diagrammatic features that we left 
behind us in Auvergne. 

The rain-swept volcanic isles of Scotland have, however, 
quite a literature of their own ; and we shall return to them 
some day later to inspect their central rocks. Although 
they are among the most recent igneous masses in our 
islands, they have suffered even more than their contem- 
poraries in County Antrim. The outlying lava-flows have 
thus been cut up into sea-stacks, showing, even in this 
detached condition, the terrace-structure of the plateaus. 

When we search among the strata of earlier periods 
for relics of volcanic action, we find ample evidence that 
again and again in the history of any country molten rocks 
have reached the surface, and have profoundly affected 
the features of our present landscapes, by reason of their 
resistance to denudation. The long line of the Ochils, so 
conspicuous from Stirling, is the edge of an ancient plateau 
of brown and purple andesites, part of a volcanic mass 
6500 feet in thickness, and extending over an area at least 
sixty miles in length.^ The Castle at Edinburgh stands 

^ Sir A. Geikie, ** Anniversary Address," Quart, Journ. Oeol. Soc, vol. 
xlviu (1892), Proceedings^ p. 70. 



DEAD VOLCANOES 1 87 

upon a crag of basalt ; while Arthur's Seat, the crowning 
glory of the city, is a black volcanic neck, surrounded by 
lavas and ash-beds, which give great variety to the surface. 
The grand wall of Salisbury Craigs is formed by an in- 
clined intrusive sheet, which has notably baked the shaly 
beds beneath it. 

Sir A. Geikie, in his two anniversary addresses to the 
Geological Society of London, 1 has given an account, rich in 
details, of the history of volcanic action in the British Isles. 
We need only in conclusion take our stand upon the narrow 
aretes of Snowdon, and look round upon the peaks and 
ridges of North Wales. Scarcely one of these prominent 
masses is unconnected with lava-flows or intrusive igneous 
rocks. The Moelwyn range above Ffestiniog, the jagged 
summits of the Glyders, the smooth-backed Carnedds in the 
north, and the twin-peaks of Yr-Eifl in the west, have all 
been weathered-out from some of the oldest volcanoes of our 
isles. The great dome of Mynydd-mawr, quite near us, is a 
neck a mile in diameter, once filled with an almost glassy 
lava, which has now become pale and white and crystalline. 
The hollows of Snowdon itself are carved through tiers of 
rhyolitic flows and tuffs, which have been traversed by 
dykes of basalt. In the compact highly silicated rocks the 
microscope shows us perlitic structure ; while spherulites, 
large and small, can easily be detected with- the naked eye. 
In walking down the Pass of Llanberis, some of the roches 
moutonnSes on the left are formed of the resisting basalt 
dykes; while above us on the right a bold columnar crag 
juts out from Esgair-felen, and sends down a loose talus to 
the road. Once this mass must have been black and glisten- 
ing, like the obsidian cliff in Yellowstone Park ; while above 
it and beneath it lay rhyolites of brilliant hues, pink and pale- 
yellow and white, with abundant layers of back glass. All 
have now undergone slow seccyndary crystallisation, through 
changes and earth-pressures which took place long subse- 
quent to their consolidation ; and they have become almost 
uniformly dull and grey. Quartz has been deposited in their 
cavities, and fills many of the fissures which have opened far 
across the hills. Many geysers and hot springs of the pre- 
sent time, aided by the minute water-plants that live in their 
basins, deposit silica as they flow ; and thus the quartz-veins 

^ Quart, Journ, Oedl. Soe,, vols, xlvii and xlviii. 



1 88 OPEN-AIR STUDIES 

of Snowdon probably represent the last stages of a long 
period of eruption. Even if we go back to the earliest strata 
of Britain, we can trace ont the sites of old volcanoes ; and 
the lavas, as well as the kind of action at the vent, appear 
to have been the same as those occurring at the present day. 
Just now, in the British Isles, we are in a period of quiet, 
such as that which prevailed through enormous ages be- 
tween the deposition of our coal-beds and the upheaval of 
the chalk above the sea ; but the far future may again rear 
cones and craters upon our smiling landscapes, and may 
bury deep in hot scoriaB and steaming lava the relics of our 
human period. 



CHAPTER VII 

A GRANITE HIGHLAND 

When we have become accustomed to examining the pro- 
ducts of volcanoes, we may take up again the lump of granite 
which we have laid aside since our earliest chapter. It con- 
tains well -formed mica, and orthoclase felspar, with its 
simple twinning, and quartz acting as a sort of ground, 
set in between the other crystals. All these minerals may 
occur in rhyolite ; we have seen that they all may be 
separated out during the cooling of that lava in the vent. 
Ill granite, moreover, they show no signs of rounding, nor 
is there a cement to bind them together ; they seem to have 
grown in place successively, and not to have been brought 
together as sedimentary materials. In fact, we may reason- 
ably suspect granite to be also an igneous rock. 

Even though the crystals may be coarsely developed, the 
felspars becoming several inches long, this is merely an ex- 
tension of the complete crystallisation which we have seen in 
the heart of massive dykes. And, when we study granite in 
the field, we shall hardly be surprised at any degree of coarse- 
ness in its texture — the masses we deal wiih. are so enormous, 
and their rate of cooling must necessarily have been so slow. 

Many of our British highlands are built of granite, and 
there we may see it, as a rock always should be seen, in its 
relation to the other masses of the earth's crust. The 
granite area will be an open moorland, such as will rejoice 
the pedestrian ; and a few well-marked summits rise above 
it here and there. 

Though the whole area is high, there are few features of 
especial grandeur. The hills are mostly rounded, with long 
curving sides descending unbroken to the valleys (see back- 
ground of Plate IX). Here and there a cirque has been cut 
out on the flank of one of these great domes ; and the clifiF, 
viewed from the side, may stand out boldly against the sky. 

Curious groups of rocks, almost like mined citadels, rise 

189 



I90 OPEN-AIR STUDIES 

from the higher slopes of many of the hills ; and long taluses 
stream down from these, until they are swallowed in the bogs 
that fill the hollows. Grass and fern and heather clothe all 
the drier portions of the mountains ; and in August the 
landscape for miles is a stretch of glorious purple. Small 
plantations of Scotch firs have been made, which climb from 
the valleys towards many of the barren ridges ; but these 
wide mountain-curves give little shelter, and sometimes the 
path of a storm-gust is marked by the red stems heaped 
together in a shattered band across the woodland. 

If we climb along the ridge between two valleys, we shall 
see a striking similarity on either hand. The spur on which 
we stand is like the back of a huge elephant, broad and 
rounded, with hardly a rock-surface to be seen. Down below, 
the streams have exposed the granite along certain steeply 
descending grooves ; but the valley-floors are covered with 
boggy alluvial flats, in which the main rivers wander in fre- 
quent curves. 

As we rise higher, we see that the hill in front of us 
assumes a nobler aspect. Its true form was hidden by the 
great uniform masses of its lower slopes ; but now bare walls 
of granite can be seen along its steeper crest, and even the 
slopes themselves are often too abrupt for taluses. Grass 
ceases to cover the huge slabs of solid rock, which weather 
out like grey inclined planes, continuing upward at the same 
angle as the valley-side below. There may be no true peak 
above the valley-head, yet this great dome in front of us has 
a grandeur of its own ; and it proves after all no easy climb 
to reach the grassy summit. 

Let us rest on the edge of one of the broad exposed 
surfaces, some 2000 feet above the sea (Plate IX). The 
grass and moss are endeavouring to get a hold on it, but 
their little tufts are easily dislodged. The rock weathers 
somewhat evenly, with shallow pits in its surface where 
the rain-storms have found weak points to begin on. If we 
look along the plane of the slab, we shall see how there are 
some parts rising higher than others, ready to be flaked 
off along joints parallel to their surface. In fact, the mass 
has a tabldar jointing, dividing it into great gently curving 
slabs ; and the forms of the slopes are largely determined by 
the angles at which these main joints lie. 

It is diflScult to cross so uniform a sheet of rock ; we 



A GRANITE HIGHLAND I9I 

may even send the whole of some hesitating flake skimming 
over the slope, before its time, into the valley. The weather 
has roughened the rock by affecting the minerals unequally, 
and the quartz stands out in little sparkling grains, while 
the wom-down felspathic areas may be partly overgrown by 
lichens. This roughness is noticeable even if we get our 
fingers into one of the tabular joints, and feel the under- 
surface of a slab. The fairly rapid destruction of the felspars 
soon widens the joint ; the mica and quartz become washed 
out as sand ; iron rust forms and stains the decaying surface ; 
and finally the brown and crumbling mass slides down the 
mountain-side, breaking up as it goes and scattering its dust 
throughout the heather. 

Sometimes these tabular joints lie horizontally, and give 
a flat-topped or gently swelling summit to the hill. Beyond 
us is a cliff in which there is all the appearance of stratifica- 
tion ; and we can see how another set of joints, unnoticed 
by us before, has determined the exposed and vertical surface 
of the rock. Two such sets of joints, indeed, occur, roughly 
perpendicular to the first series and to one another; and 
each set is in turn brought into play, according as the local 
agents of denudation work most persistently in one direction 
or in another. 

The uniformity of structure of the granite mass has 
checked the formation of conspicuous peaks ; but here and 
there, as we noticed from afar, a few rocks rise above the 
general curves of the long moorland. These masses are 
called tors in Devonshire, and are easily seen to be in all 
stages of decay. The tabular joints control the outlines of 
some, and the blocks fall away from beneath certain of 
the layers, leaving ledges projecting out above our heads. 
In other cases the three main sets of joint-planes have 
divided the mass into fairly regular blocks, almost like the 
squared stones of buildings; and the weather has widened 
some of the vertical cracks and has produced deep gullies 
through the tor. Hence the castellated effect of many 
of these masses at a distance. But every stone has be- 
come rounded on its edges, and crusts of decaying material 
cover the surfaces and crumble away when they are struck. 
Gradually the well-formed block, bounded by sharp joint- 
surfaces, becomes reduced to a boulder, unstably perched 
upon the rock below. A little wedging of frost, a little 



192 OPEN-AIR STUDIES 

further crumbling of its lower surfaces, and it falls readily 
upon the talus, to be slowly buried there in the grass. All 
round the present tors on Dartmoor, the taluses are far more 
remarkable than the upstanding rocks. They stretch away 
in long concave curves from these diminished crags, these 
relics of old peaks, and thus encumber miles of moorland. 
The former greatness of what we now call tors is to be seen 
in the blocks which lie everywhere strewn amid the heather. 

All stages can be traced between the typical tor, standing 
up so quaintly on the summit of its talus-cone, and the 
huge rock-domes which we have here before us on our high- 
land. When once cirques begin to be formed in the moun- 
tains, the mass between their retreating curves is doomed. 
Gradually the convex table of the summit is reduced to 
a flat-topped rock, girt about with cliffs; at its base the 
taluses stream down in all directions, the great boulders being 
heaped on one another as if shattered by the catastrophe of 
a moment ; and at last even the table becomes worn out into 
pinnacles, which go down one by one into the encroaching 
hollows of the combes. The scene reminds one of the decay 
of some great empire, as the changes of the times draw away 
the states on all sides, leaving the centre of power still more 
prominent, by reason of its very isolation. 

In Cornwall, some of the rock-pillars that are left behind 
seem at first as if built by human agency, rather than worn 
out of a once solid mass. In the Mourne Mountains, again, 
there is a group of pinnacles (fig. i6) fantastically flanking 
a little canon, beyond which there lies a circular hollow set 
about with similar columns. We seem to see the vestibule 
and the central hall of some old temple ; and it is hardly 
strange that legends should still hang round these wind- 
swept recesses of the rocks. 

In all such cases it is the horizontal jointing that gives 
the effect of masonry ; but this structure is not aided by any 
difference in the texture of the layers, which might cause 
the hillside to weather out into steps and terraces. All 
round us the rock slips evenly away, boulder by boulder, 
slab by slab, and these great uniform slopes are the result. 

As we cross a smooth exposure of the granite, we see 
little dykes and veins, usually of more finely grained material, 
cutting across the main mass of the rock. Some of these 
even cross one another ; and often the fissure that has ad- 



A GRANITE HIGHLAND 193 

mitted the more recent of two veins has been accompanied 
by a movement, which haa shifted the broken edges of 
the earlier vein, until they are no longer opposite to one 
another. We may note that these dykes consist also of 
granite, which is often very compact in texture ; and even 
in them the crystallisation can sometimeB be seen to be 




i BlVBR, MOURNE 

Mountains. 
.(Phot'jgraphedbsMr.S. Welch.) 



coarser in the interior of the dyke and distinctly more 
delicate on its margins. 

We are evidently in the presence of an igneous mass 
that haa cracked open more than once since its consolida- 
tion. Material, still molten, was always at hand to ooze up 
from below and to fill up the fissures as fast as they were 
made. But the conditions of cooling were slow even in 



194 OPEN-AIR STUDIKB 

these veinB, siiice they have become oompletehr, though 
often minutely, crystalline. The lower blocks of the con- 
solidated gramte may have been again and again absorbed 
into the liqnid mass below, before the whole finally became 
solid. A sabterranean reservoir may have existed, com- 
parable to the lava-lake of Kilanea (p. 156), which now eats 
away, now reconstructs its walls; and in time the heat 
diminished, allowing the whole contents to crystallise, nnder 
conditions of far higher pressure than are experienced by 
any lava near the sorface. 

On many of onr slabs of granite we see porphyritic fel- 
spar crystals, which must have developed previously to the 
finer material of the ground. These long orthoclase crystals 
are especially frequent in the granites of Devon and Cornwall, 
and the shorter pink crystals of the rock of Shap in West- 
moreland have made it famous as an ornamental stone. Do 
they represent a period of greater earth-pressure and still 
slower cooling, when the rock began to crystallise on a 
grander scale? Was the mass then remelted, these large 
felspars being left to tell the tale of its first and unsuccess- 
ful efforts? These are some of the questions which arise 
when we try to conceive the operations that take place in a 
deep-seated caldron of molten rock. The abundant develop- 
ment of quartz is probably connected with the imprison- 
ment of water under pressure ; but further experiments on 
its artificial production are required to elucidate this point. 
Now and then we can trace, in veins and knots of deposited 
material, the course of hot liquids and vapours which subse- 
quently passed through the rock ; the older minerals have 
been deprived of some of their constituents, and new ones 
have arisen from the interaction of the invading substances 
and the granite. In this way minerals containing fluorine 
often arise, such as Topaz and Fluorspar; and black hard 
radiating rods of Tourmaline, a complex silicate and borate, 
grow out from centres of decay and spread through the rock 
like a disease. During the destruction of former silicates, 
silica is often set free, which crystallises as additional, or, as 
we say, "secondary" quartz. On Dartmoor whole rock- 
masses occur converted thus into tourmaline and quartz. In 
ComwaU, again, tourmaline is commonly formed, apparently 
by the action of boric acid vapours, on the sides of the 
granite veins ; and, in the little inlet of Nanjisal, near the 



A GRANITE HIGHLAND 1 95 

Land's End, an altered granite occurs, in which the red 
porphyritic felspars are reduced to mere shells, their ex- 
cavated interiors being partially or wholly filled up again by 
secondary quartz ; while the more finely-grained ground is 
replaced by a mass of delicate tourmaline needles, set in 
granular lumps of quartz. The whole of this ground is of 
secondary origin, the former crystals of quartz and felspar 
and mica having been attacked, and part of their constituents 
having been used up again during this thorough process of 
reconstruction. 

This shows how profound mineral changes may go on even 
in deep-seated and apparently protected masses. Minerals 
are deposited around the fumaroles in volcanic craters, where 
the vapours escape from the interior of the earth ; but the 
chemical action of these gases will be much more extensive 
when influenced by the high temperatures and pressures in 
the interior of the crust. Whether the temperature is suffi- 
cient to keep them in the gaseous condition, despite the pres- 
sure, or whether the pressure condenses them into liquids, 
they will permeate the heated rock-masses and carry on a 
series of " mineralisations." In the short time at our dis- 
posal for the performance of a laboratory-experiment, it is 
impossible to imitate all these results of prolonged natural 
action ; but many rock-forming minerals have now been 
artificially reproduced, particularly by a brilliant group of 
chemists and mineralogists in IVance, stimulated by the 
work of MM. Pouqu^ and L^vy. 

There can be no doubt, however, that the principal 
minerals in our granite, and the structures of the mass, 
from the porphyritic crystals to the shrinkage -joints, are 
due to its consolidation from a state of fusion. The study 
of a series of rhyolites will show us how it is no step, but 
merely a continuous passage, from the most " stony " of 
these rocks to the fine-grained veins of granite ; and from 
these we can pass easily to the most coarsely developed 
masses. It is natural, then, to conclude that in our granite 
highland we have the weathered-out contents of a caldron 
which once underlay a volcano or a series of volcanoes. 
These volcanoes would have erupted rhyolites; and the 
extinction of the area would have been due to the con- 
solidation of the contents of the caldron by loss of water or 
by diminution of the heat supplied to it. 




196 OPEN-AIR STUDIES 

Many snch caldrons mnst exist, however, without their 
molten matter attaining the surface of the ground ; and it 
is difficult in any case to trace a connexion between the 
surface-products of a volcano and its highly crystalline basis. 
The cones and lava-flows must be swept away by denudation 
before we can get at the underlying rocks ; and it is only in 
rare cases that some deep valley, or the borings of a mine, 
will reveal to us the two classes of products in their true 
relations to one another. 

Occasionally the huge central neck of some old volcano 
will serve us almost as well. Professor Judd^ has again 
and again emphasised the connexion between glassy and 
partly glassy lavas and the most crystalline central masses 
in the complex and denuded volcanoes of Mull and Skye. 
Messrs. Hague and Iddings^ have similarly shown the lavas 
and completely crystalline rocks of Washoe in Nevada to 
be a continuous series, and have supported their evidence 
by a series of chemical analyses. Even the great majority 
of Continental observers, who felt that such a connexion 
was not established in their own countries, have now ac- 
cepted the view that highly crystalline granitic rocks may 
be forming at the present day beneath our feet. Modem 
examples are difficult to get at— that is all. In the Hebrides, 
however, the wild west showers and the driving winds of 
the Atlantic have cut down into the central igneous masses, 
and have exposed coarsely crystnlline rocks of a compara- 
tively recent geological age. 

If the broad moorland on which we wander is a true 
igneous mass, surely it must have produced, like a dyke, 
some effect upon the rocks which border on it. Let us 
cross the watershed, and descend from the high tors and 
towers, until we meet with some material different from 
the granite. 

A few miles down the valley that we have selected, 
its walls become scarred with a series of ridges of dark 
rock, which run down parallel to one another, projecting 
from the grassy slope. They are occasionally curved and 
folded, and present all the appearance of uptilted strata. 

' "The Secondnry Rocks of Scotland," Qttart. Joum, Oecl, Soc., vol. xxx 
p. 276 ; " Volcanoes," p. 142 ; &c. 

^ " On the Development of Crystallisation in the Igneous Rocks of 
Washoe, Nevada," BuUetin U, 8, Oed, Survey, No. 17 (1885). 



A GRANITE HIGHLAND 197 

Hard by, there is a large quarry, opened to obtain the 
granite ; and at the lower end of it the dark rock appears 
as a projecting bluff, cut round and neglected by the work- 
men. The contrast of the two rocks is striking; and we 
have here come to the edge of the granite mass. 

A few moments* inspection shows us that the pale pink 
and orange granite has almost wrapped round the darker 
rock ; a dyke of granite has run out at the junction, and 
can be seen wandering away up the quarry-face. The dark 
rock is shaly, but its delicate planes of division are covered 
with gleaming plates of mica ; and fine threads and sheets 
of what appears to be quartz occur freely in between the 
layers. 

Some of these filmy sheets actually are composed of 
quartz ; they agree in character with the deposits in many 
of the cracks that we observed high up amid the granite. 
But others are seen on close inspection to contain felspar ; 
here and there a mica flake occurs ; and these delicate bands 
are really offshoots from the granite. 

At another point small veins run off distinctly from 
the main mass across the bedding of the shaly rock, thus 
imitating the larger dyke. There can be no doubt as to 
the character of the junction which we see here exposed. 
The granite is, as we say, intrusive in its stratified sur- 
roundings. 

If we now climb the slope, we shall be able to trace 
the line of junction, bending now this way, now that, and 
shall find ample evidence of its irregular character. More 
than this, the granite near its margin contains numerous 
dark flecks and patches, and these prove to be pieces of 
its neighbour, which have actually become picked off and 
partly melted. The delicate intrusions at the junction down 
in the quarry have prepared us for this intermingling of 
the rocks ; and even the great projecting bluff is, as we saw, 
almost completely surrounded by the granite. 

Sometimes the intrusion of veins along the bedding- 
planes of the shale has produced a rock composed of 
alternating layers of dark micaceous shale and pale pink 
granite. This would be a difficult material to understand 
if we saw merely a loose specimen of it, instead of collect- 
ing it for ourselves. The whole hillside now above us gives 
a wonderful picture of the attack of the molten rock, when 



1 98 OPEN-AIR STXTlIES 

far beneath the surface of the ground, npon the older masses 
into which it flowed. 

If this seems simple to understand, when we see the 
network of veins before os in the field, and when we con- 
sider its similarity to what is revealed by the denadation 
of a volcanic centre, yet this version of the origin of granite 
is really very modem. James Uatton, the great Scotch 
geologist, was the first to prove, by producing similar evi- 
dence, that granite was an igneous rock, his observations 
being made in Glen Tilt in 1785. Even in our own day, 
distinguished authors have asserted that rocks of granitic 
structure could be formed as deposits from hot solutions, 
perhaps at the bottom of the sea. A kind of solution there 
may be, when we consider the water that permeates the 
mass, even when at its greatest heat; but of the former 
molten condition of the rock there can be no reasonable 
doubt. 

The study of the fragments of other rocks picked up and 
surrounded by granite has been carried on microscopicsdly in 
several countries ; and we find that some constituents of the 
included rock may become melted to a glass, while others 
are left but little injured. Ultimately the latter minerals 
remain alone, scattered through the granite, all trace of 
their mode of origin having disappeared. It is clear that 
this selection of minerals, dependent on the greater fusibility 
of some of them, may provide the granite, when it con- 
solidates, with constituents of a very puzzling character. 
The porphyritic crystals of lavas have no doubt often been 
derived from similar foreign sources (p. 168); and it is 
convenient te speak of all such objects, when their origin 
can be traced, as derived crystals. 

The dark rock in contact with the granite now demands 
attention. It has some characters of a shale, as we have 
already noted, but is remarkably crystalline. Some layers 
are crowded with distinct flakes of mica; in others dark 
specks and rods stand out in a fine grey micaceous 
ground. We must follow this mass step by step down the 
valley. 

As we recede from the granite, the amount of con- 
spicuous crystallisation diminishes, and the whole rock is 
duller and more compact. At last, perhaps a mile away, 
we find it as an ordinary shale, and we may be so fortunate 



A GRANITE HIGHLAND 1 99 

as to detect traces of marine animals in it. At one time, 
then, these muddy strata were deposited in the sea. They 
have been uptilted, and the granite has flowed into them ; 
is it not, then, likely that the igneous rock, with its slow 
cooling, and the escape of liquids and vapours from it, has 
produced the crystalline condition of the mass along the 
junction ? 

We use the term metamorphism to express the pro- 
duction of such extensive changes, of which heat and 
pressure, singly or both together, have been the causes; 
and we say that such changes as we now are studying 
result from contact-metamorphism. Limestones become 
crystalline when in contact with great igneous masses, 
silicates rich in calcium becoming developed in them, often 
by an interchange between their constituents and those 
of the invading rock.^ Sandstones become hardened and 
compacted, and any fragments of felspar occurring in them 
become more or less melted and form a glass between the 
grains of quartz. Clays and shales become baked into a 
dark flinty condition, some of the particles actually melt- 
ing; here, again, any felspathic grains will aid the pro- 
cess, while chemical combinations become set up which 
result in the formation of new crystallised minerals in the 
mass. 

Two of the commonest minerals which arise from the con- 
tact-metamorphism of mixed materials, such as impure clays, 
are a pale mica, containing a good deal of water in its com- 
position, and pink-red or pink-brown garnets. The garnet 
series consists of silicates of various metals, the latter re- 
placing one another without altering the type of crystallisa- 
tion. Garnets belong to the cubic system, and commonly 
appear as somewhat spherical bodies on the fracture of the 
rock containing them. In reality, the most usual form has 
twelve faces, its high symmetry giving it a granular aspect 
when it is developed on a small scale. The reddish garnet 
so frequently occurring is called Almandine, and is a silicate 
of aluminium and iron ; it easily scratches our knife-blade, 
and, from its colour, can be picked out readily by the eye. 

Another substance, however, has assembled to form the 

^ See, for instance, Johnston-Lavis and Gregory, " On Eozoonal Structure 
of the Ejected Blocks of Monte Somma," TVoruf. Roy. DuUvn Soc,, ser. 2, 
vol. V (1894), p. 259. 



200 OPEN-AIR STUDIES 

dark spots and patches. Some of these are composed of 
materials that could not get sufficiently well aggregated to 
form recognisable minerals. But others have reached the 
stage of fairly outlined rods, like little pieces of slate-pencil. 
These have been shown by chemists to be Andalttsite, one of 
the forms adopted by crystallised aluminium silicate. This 
is precisely the mineral that one might expect to arise from 
the prolonged heating and compression of a clay, seeing that 
clays are almost entirely made of aluminium silicate com- 
bined with water. Andalusite often developes in radial 
bunches, and sometimes gets rid of the impurities which 
give it its dull colour ; it then appears as sharp-edged four- 
sided little rods, lying, like wooden matches, in the ground- 
work of compacted clay. 

It is pleasant to observe in microscopic sections of the 
products of contact-metamorphism how large a part is played 
in the resulting crystals by the impurities caught up in them. 
The crystallising matter collects round a number of stolid 
unaffected particles of the original rock, and tries, as it were, 
to elbow its way in between them ; finally something like a 
crystal is built up, the faces being in reality very ill defined, 
and the great bulk of it being formed of matter which could 
not be thrust out from it. 

The neat little match-like crystals of andalusite which 
occasionally occur, as in the altered shales of Skiddaw, have 
succeeded in arranging the impurities within themselves into 
two sheets, connecting the opposite pairs of long edges of 
each rod, and also into the form of five columns, one running 
down the central line of the rod and one down each long 
edge. The result, when the crystal is broken across, is that 
a black cross appears, with patches at its ends and at the 
centre ; and this variety of andalusite has consequently been 
named Chiastolite, or "cross-stone." 

Metamorphism along a plane of contact is naturally a long 
process, and minerals are developed and succeed one another 
just as they do during the slow crystallisation of an igneous 
rock. Thus Miss Gardiner^ noticed that, in the zone of 
alteration round a granite in the south of Scotland, the 
garnets appeared first, as was shown by the fact that they 
included none of the other products of metamorphism. The 

^ " Contact Alteration near New Galloway," Quart. Journ. Geol. Soc, vol. 
xlvi (1890), p. 579. 




A GRANITE HIGHLAND 20I 

chiastolite, however, included the garnets; and the micas 
were formed against and bent round both these minerals. 

A large number of the little irregular black spots that 
occur in altered shales are really due to mica, which can be 
traced in all stages of development. After all, in the great 
majority of these rocks, as we walk across them in the field, 
mica is by far the most striking feature. 

Messrs. Harker and Marr ^ have shown how about thirty 
species of minerals have been developed in various rocks 
round the granite of Shap in Westmoreland. In many 
cases the molten mass acted upon older igneous rocks; 
but at least twenty- one of the mineral species arose 
in the adjacent shales and limestones. The formation 
of both orthoclase and plagioclase felspars in these sedi- 
mentary rocks is the most noteworthy point in the results 
obtained. 

The zone of alteration round the Shap mass is about 1 2(X) 
to 1 300 yards wide, the granite, as exposed at the surface, 
having a diameter of about 2500 yards. In most cases, the 
constituents of the rocks close to the contact have become 
entirely rearranged. The minerals that had already been 
formed in the adjacent igneous rocks by processes of decay, 
such as carbonates and hydrous silicates, were the first to 
suffer from the metamorphic action. The authors believe 
that no transference of materials from one rock to another 
has occurred in this case, and that the new crystals, even 
the wonderful assemblage of pyroxenes, and amphiboles, and 
garnets rich in lime, in the altered limestones, have arisen 
by the creeping together of materials already present in the 
sedimentary rock. They show, moreover, in certain measure- 
able cases, that these substances have not shifted their posi- 
tions by more than one-twentieth of an inch; the new minerals 
have, in fact, been built up out of older ones which were 
practically in contact.^ 

We have now looked into the past history of our granite 

^ "The Shap Granite, and the associated Igneous and Metamorphic 
Rocks," Quart. Journ. Geol. Soc, vol. xlvii (1891), pp. 292-325; and "Sup- 
plementary Notes on the Metamorphic Hocks around the Shap Granite," ibid.f 
vol. xlix, p. 359. 

'^ The literature regarding the products of contact-metamorphism is admir- 
ably summarised by F. Zirkel, "Lehrbuch der Petrographie," 2nd edition, 
Band ii, p. 82, &c. For British examples, see J. J. H. Teall, " British Petro- 
graphy," p. 373. 



202 OPEN-AIR STUDIES 

highland, and have pictured it as a molten mass, working its 
way into the surrounding strata and imprisoned deeply under- 
ground. At present its denudation and decay offer us many 
interesting features, especially since the sedimentary rocks, 
with which we are already familiar, are so largely derived 
from the decomposition of igneous ones. 

When examining the tabular joints on the shelving sur- 
face of the mountain, we saw how the rock was going to 
pieces through the attacks of the weather upon its con- 
stituents. Analyses show that the soda is carried away most 
rapidly from a decomposing granite, and the potash far more 
slowly, both these substances being extracted from the fel- 
spars. If lime is present, it is carried off at least as quickly 
as the soda. In any case, part of the attacking water be- 
comes combined with some of the constituents of the granite, 
and the proportions of silica, alumina, and iron oxide remain 
about the same, the silica generally increasing slightly. But 
a great physical change accompanies these chemicsJ ones ; 
the surfaces of the felspars become coated with fine kaolin 
dust, and at last those developed porphyritically can be lifted 
out of the rock-mass. Their cleavage-surfaces similarly be- 
come powdery, and the crystals themselves break easily into 
little blocks. The micas, especially the biotites, take up 
water and alter into still softer products, such as chlorites. 
Any hornblende that may be present similarly passes into 
soft green powdery products. A certain amount of iron 
oxide is set free, which takes up water and forms brown 
streaks and films ; while the smaller felspars pass entirely 
into powdery kaolin, like flour. The stubborn quartz, now 
dusted over with kaolin, rolls out loose into the ddhris of the 
slope. Its original granular form fits it admirably for fur- 
ther wanderings, and it already resembles grains of sand. 

The great streams of solid matter washed down from 
the decaying cliffs can be appreciated when we look up at 
them from the floor of our valley. The little torrent in the 
hollow is busy sifting them out, and already we have banks 
of sand amid the alluvium, from which the fine clay has 
been removed. Much of this sand, however, when we run 
it through our fingers, is composed of little lumps of 
granite, which are ready to be further broken down, but 
which still contain all the constituent minerals associated 
together. 



A GRANITE HIGHLAND 203 

The finer matter, washed away and laid down in the 
alluvial levels a few miles lower down onr valley, is divided 
into particles consisting of separate minerals, the bnlk being 
kaolin with embedded grains of sand. At this point com- 
mercial companies have set up works for its further artificial 
subdivision, and the pure white kaolin is washed out into 
tanks and finally sent off to the Potteries as china-day. 
The natural agents would have finally sorted out the 
materials on the sea-coast (p. ICX)); but by that time other 
ingredients would have got in, and the kaolin would be no 
longer pure. It is coloured on the shore by iron oxide, by 
iron sulphide, by decaying animal and vegetable matter; 
it thus becomes merely common clay. 

Here then we are at the source of our sands and clays, 
two great groups of sedimentary rocks. We can, in fact, 
trace them back to igneous masses. Even the salts of lime 
that are carried away from our highland in solution go to 
furnish the sea with calcium sulphate and calcium carbonate, 
from which the lime is again extracted by organisms for the 
construction of the calcium carbonate of their shells and 
skeletons. Thus granitic rocks also help to form the 
great beds of limestone, the shell-banks and the coral- 
reefs, which constitute our third main group of sedimen- 
tary deposits. 

When we picked up our granite specimen at the outset 
of this chapter, we compared its constituents with those of 
rhyolite. A typical analysis of rhyolite- obsidian, the most 
glassy rock of this series, has been given on p. 166. If we 
powder up a good lump of granite, so as to get all its con- 
stituents well mixed in average proportions, we shall find 
that through its analysis it is also comparable to rhyolite. 
From the point of view of our chemist, the two rocks would 
be practically identical ; the difference is one of structure, 
arising from different conditions of temperature and pres- 
sure during consolidation ; and thus every variety of rhyolite 
can be paralleled in chemical composition by a possible 
variety of granite, or vice versd. 

Let us take two granites from the British Isles as our 
examples, expressing the constituents, as is usual, in the 
form of oxides. The first one consists of quartz, orthoclase, 
albite, muscovite, and a little biotite, and is a typical " white 
granite " ; the second is the famous " red granite " so largely 



204 



OPEN-AIR STUDIES 



used for omainental building, and contains similar consti- 
tuents to the other, muscovite being, however, absent. 



Silica 
Alumina . 
Iron oxides 
Lime 
Magnesia 
Soda 

Potash . 
Loss on ignition 



. Average of eleven 
j analyses of Granite 
|of the Leinster Chain, 
Ireland. (Ur. S. 
Haughton.) 



72.07 

14.81 

2.25 

1.63 

0.33 
2.79 

5.II 

1.09 



Total 



100.08 



n. 

Granite of 
Peterhead, 

near Aberdeen. 

(J. A. Phillips.) 



73-70 

14.44 

1.92 

1.08 

trace 
4.21 

4.43 
.61 



100.39 




The rocks commonly called ** granite " in the building- 
trade vary, however, very widely in mineral constitution, 
though they agree fairly in structure ; and they are known 
to geologists under distinct names. It is highly desirable 
that architects and others should recognise the differences 
between them, since the degree to which they may be 
attacked by weather, as well as the convenience with which 
they can be worked, depends largely upon their mineral 
constitution. 

If our typical granites, as above analysed, correspond to 
rhy elites — ^if, indeed, a granite caldron would clearly erupt 
rhyolite at the surface — are there no deep-seated masses 
corresponding to the other types of lava ? As a matter of 
fact, aJthough the word ^^ granite " is familiar to all of us, 
it covers only one out of four great groups of completely 
crystalline igneous rocks. These are : — 

I. Granite. — This rock contains from 65 to 75 per cent, 
of silica, corresponding to rhyolite in composition. Its 
characters have been sufficiently described above, with the 
exception of its specific gravity. This is higher than that 
of rhyolite, owing to the complete crystallisation, but lower 
than that of other rocks of similar structure, owing to the 
small amount of heavy oxides that granite contains. The 
specific gravity is thus about 2.65. 



A GRANITE HIGHLAND 205 

2. Syenite. — Here we have only some 60 to 65 per cent, 
of silica, with potash, as in granite, in excess of soda. The 
name is from Syene, the modem Assouan ; but the rock 
of that area, extensively used by the ancient Egyptians, is 
properly a Hornblende-granite in our modern classification. 
Oaesalpinus,^ writing at the end of the sixteenth century, uses 
** Syenites " and " red granite " {granitum rubrum) as terms 
having the same meaning ; but Syenite is now restricted to 
a rock practically free from quartz. Orthoclase felspar, and 
an amphibole, or a pyroxene, or a mica, are the important 
constituents. The rock is a granite without suflScient silica 
to form quartz, and thus consists typically of two minerals 
only. It is often red, owing to the colour of the prevalent 
crystals of orthoclase. Its specific gravity is about 2.75. 
It is obvious that this is the deep-seated representative of 
trachyte. 

3. Diorite. — The silica here runs from 70 to 55 per cent., 
with soda in greater amount than potash. The name is from 
Stoptfft), " I distinguish," because of the clearness with which 
the two main constituents stand out from one another. 
Plagioclase felspar (albite, or oligoclase, or even labradorite) 
takes the position that is occupied by orthoclase in the 
syenites. In some cases the silica is sufiicient to form quartz, 
and the rock is called a Quartz-Diorite, The quartz-diorites 
are probably quite as abundant on the globe as the true 
granites. TyP^^^^ diorites consist of oligoclase and horn- 
blende, or mica, or pyroxene ; those varieties with least silica 
contain more lime than the others, and the crystals in these 
are often labradorite and augite. The colour of the rock is 
usually white spotted with black. The specific gravity is 
about 2.80 in those varieties rich in silica, and 2.95 in those 
rich in lime, magnesia, and iron oxides. The diorites thus 
cover in their characters the same range as the great group 
of andesites. 

4. Olivine-Oabbro. — Here the silica-percentage is from 
55 to 45, and the heavy oxides are of increased importance. 
The name Gabbro is of obscure Italian origin, a Tuscan rock 
being spoken of in the last century as ^^ granito di Gabbro " ; 
but of late it has been reserved for rocks consisting of a 
plagioclase and a pyroxene, which would come with us under 
the head of " pyroxene-diorite." Olivine-Gabbro contains a 

^ "De Metallicis,'' edition of 1602, p. 94. 



2o6 



OPEN-AIR STUDIES 



plagioclase (labradorite or anorthite), a pyroxene (or rarely 
hornblende or biotite), olivine, and magnetite. The olivine 
marks the decrease in silica that has occurred, while the iron 
oxides have been able to crystallise out abundantly, instead 
of being worked up into silicates. They are usually associated 
with oxide of titanium, giving rise to titaniferous iron ores. 
The rock is darker in colour than common diorite, and is often 
blue-black through the abundance of pyroxene or amphibole, 
and through the fact that the felspars have become dulled 
and grey by internal chemical alterations. The large crystals 
of pyroxene in coarse varieties of the rock give a somewhat 
metallic lustre to certain portions. The speci6c gravity is 
about 2.90 to 3.00. The mass is commonly very tough and 
difficult to break, especially where the felspars are altered 
into new lime-silicates and where the pyroxenic constituent 
is abundant. Clearly olivine-gabbro is merely the completely 
crystalline representative of common basalt. 

Hence, with the knowledge that these crystalline types 
of rock exist, we may enlarge and modify our classification 
of igneous rocks (p. 1 7 1 ) so as to include them. If we take 
the completely crystalline types as the bases of four rock- 
groups, we may use the minerals developed in them to guide 
us in our arrangement ; this is a character that we could not 
previously employ when we were dealing with only partly 
crystalline materials. 

Summary op Igneous Rocks. 



Principal Mineral 
Confitituents. 


Name and 

approximate Specific 

Gravity. 


Approximate 

Percentage of 

Silica, 


Glamy representative 

and its Specific 

Gravity. (See also 

Table on p. 171.) 


Quartz, 

Orthoclase, and 

Muscovite (or 

Biotite, or 

Hornblende). ^ 


Granite 
2.65 


} " { 

• 


Bhyolite-glasB 
2.30 


Orthoclane and ^ 
Hornblende (or 
Biotite, or Soda- 
pyroxene). 


Syenite 
2.75 


} «' { 


Trachjrte-glasB 
2.40 



A GRANITE HIGHLAND 



207 



Summary op Igneous Rocks — ecmtinued. 



PrinciiMl Mineral 
Constituents. 


Name and 

approximate Specific 

, Gravity. 

1 


Approximate 

Percentage of 

Silica. 


Glassy representative 

and its Specific 

Gravity. (See also 

Table on p. 171). 


Oligoclase (or ' 

Albite) and 

Hornblende (or 

Pyroxene, or 

Biotite) ; often 

Qnartz. 

Labradorite, 

Augite (or 

Rhombic 

Pyroxene), and 

Magnetite. j 


^ Diorlte (often 
! Quartz-Diorite) 

Type rich in 

silica. 

2.85 

Diorlte 

Type poor in 

silica. 

2.90 


- 6s . 

J ■ k 


Andesite-glass 

Type rich in 

silica. 

2.50 

Andesite-glass 

Type poor in 

silica. 

2.65 


Tiabradorite ^ 
(or Anorthite), 
Augite, Olivine, 
and Magnetite. . 


Glivine-Gkibbro 

1 


} =« { 


Basalt-glass 
2.75 



In all these types, the specific gravity usually becomes 
lower on the alteration of the rock, owing to the introduction 
of water and the formation of hydrous silicates, together with 
the removal of some of the heavy oxides in soluble combi- 
nation. 

Suppose, now, that we bring home three specimens of 
distinctly crystalline character, collected in the field, and 
that we wish to assign to them distinctive names. The first, 
for example, is made of orthoclase felspar and augite, with 
a specific gravity of 2.77. This may obviously be called an 
" Augite-Syenite." 

The second consists of quartz, a plagioclase felspar, biotite, 
and pink garnet ; its specific gravity is 2.90, being no doubt 
raised by the presence of the heavy garnets. This rock is 
evidently a " Quartz-Diorite with garnet." 

The third specimen consists of a dull white plagioclase, 
augite altering into somewhat fibrous hornblende, a few dark 
soft lumps, which may be decomposed olivine, several chloritic 
areas, and conspicuous and lustrous patches of magnetite. 
The constituents in this rock are difficult to determine, and 



208 OPEN-AIR STUDIES 

we may be especially doubtfnl as to the former presence of 
olivine. The chlorite may have arisen from the decay of the 
hornblende, or from biotite, and the whole mass has evidently 
been extensively altered. We most place it as a possible 
Diorite or Olivine-Gabbro. A convenient field-name for all 
decomposed crystalline rocks of this type, poor in silica, with 
greenish alteration-products, is Diabase, an old term revived 
in this sense by Hausmann some fifty years ago. 

For granites we may go to the long slopes and castellated 
tors of Dartmoor ; or away west to the barren Cornish up- 
lands ; or to the great chain of Leinster, which is some sixty 
miles in length, and from 1 5CX) to 3000 feet above the sea. 
In Scotland, from Perth northwards, there are numerous 
wide bosses of ancient date ; but none are more interesting 
than the Red Hills of Skye, which are among the more 
recent igneous masses of the British Isles. The granite is 
here somewhat minutely crystalline, and probably it is only 
the upper part of a great intrusive mass. But its dome-like 
outlines are characteristic, as also are the broad enveloping 
taluses which flank these isolated hills. Far away, from the 
rugged shore of Balmacarra, the huge curved back of Beinn 
na Cailleach of Broadford can be seen against the sunset, 
with its sea-front scarred and carved into one steep cliff. 
Beyond it is the bold smooth cone of Glaraaig, with Marsco, 
almost as simple in its outline, rising in the midst of gloomier 
and serrated hills. When we actually walk up the glen 
beneath these pink-red masses, we are apt to underestimate 
their height; already we see how weathering is wearing 
away the relics of a crag on Marsco, and is converting a 
mountain-peak into a round-backed granite moorland. 

The former dignity of most of our granite ridges has 
thus been lost to us ; but the Moume Mountains in County 
Down in Ireland preserve a remarkable degree of steepness. 
Here, again, it is the massiveness of the scenery that attracts 
us, rather than any special detail ; but the valleys are still of 
bold proportions, and deepen rapidly as we descend from 
their heads towards the sea. We view the open water from 
between two steep walls, where slabs of granite are exposed 
amid an expanse of heather ; and above us the rock looms 
up into wild tors, which send down blocks for some 2000 
feet into the hollows. If we stand upon one of these silent 
crests, we may see the western masses like huge grey walls 



A GRANITE HIGHLAND 20g 

in the haze of a summer afternoon. Scarcely a break or 
ledge is now discernible, except where the white water of 
some mountain-lake seems to float like a cloud in the great 
gloom. 

The date at which the Mourne granite intruded into the 
shales and sandy strata which surround it is probably, like 
that of the Skye masses, comparatively recent; but even 
later granite ridges are observable in the Alps, and will be 
inspected by us in a subsequent chapter. 

Granites tend to graduate into quartz-diorites, even in 
the same rock-mass ; but the diorites rich in silica produce 
similar scenic features to those of granite areas. The 
" granite " of Beinn Cruachan above Loch Awe, in Argyll, 
is largely a quartz-diorite ; and this great mass, 3600 feet 
above the sea, has some twelve broad valleys carved down 
in it. The bare rock shows itself in a few cliff-ledges and 
towards the long ridge of the summit ; but for the most part 
the hollows have smoothly curving slopes and floors, covered 
with grass or brown stretches of mountain-bog. 

Syenites are decidedly rare rocks, one of the few British 
examples being that of Groby, at the south end of Charn- 
wood Forest in Leicestershire. The quarries cut in this 
district are of great size, and the stone is broken up and 
sifted by machinery through coarse sieves made of iron 
plates perforated with circular holes. It is then exported 
throughout all eastern England for road-metal, and promises 
to become one of the best known of our igneous rocks. Its 
delicate pink-purple and greenish tints make it easily re- 
cognisable in the wayside stone-heaps. 

The diorites poor in silica are exceedingly common rocks, 
especially in the form of dykes. These rocks form the bulk 
of the " Greenstones " of older authors, although this term 
became at one time carelessly applied to practically any 
igneous rock that was not obviously a granite. A bold mass 
of diorite forms Hanter Hill on the border of Herefordshire 
and Eadnorshire ; and Stanner Hill, on the other side of the 
Kington road, is a similar dark rock penetrated by fine- 
grained granite. The glaciated ridge of Mynydd-y-Gader, 
which forms a fine foot-hill to the wall of Cader Idris, 
consists also of a coarse augite-diorite. Dykes and intrusive 
sheets of this rock run along the whole of the middle ledges 
of the mountain, penetrating the tuffs and altered shales. 





210 OPEN-AIR STUDIES 

These dark masses, in which the augite stands out con- 
spicuously on weathering, form a striking contrast to the 
pale grey rhyolites and to the andesites rich in silica, which 
form the great cliff of Cader Idris, and which also emerge 
in a long band farther north. 

Carlingford Mountain, on the south side of the sea-inlet 
which reaches up to Newry in County Down, is composed 
of a dark pyroxene-diorite, the typical "gabbro" of most 
authors (see p. 205). The high ridge has weathered with a 
serrated outline, and great bosses and steps of rock occur all 
across the upper slopes. The joint-surfaces are less regular 
than those of granite, and a corresponding irregularity of 
surface is the result. As a picturesque mass, Carlin^ord 
Mountain is far more impressive than the whole group of 
the Mournes across the water ; and this nobly broken char- 
acter is found to be characteristic of all high areas of gabbro. 
The rock is deep grey, passing towards black, and the sur- 
faces of augite and rhombic pyroxene give it patches of 
almost metallic lustre. 

The olivine-gabbros find their giandest British develop- 
ment in the heart of Skye. The rock is there typically dark, 
blue-black to brown-black, with similar structure to that of 
Carlingford. Its joints allow of deep vertical clefts being 
cut in it ; but it does not flake away evenly like granite. Its 
felspars, being devoid of alkalies, do not break down like 
orthoclase and albite ; and their products of decomposition, 
which are usually hydrous silicates of lime and iron, tend 
rather to consolidate and strengthen them. The uniformity 
of decay noticeable in granite does not occur, therefore, in 
olivine-gabbro, although the olivine itself alters into dusky 
serpentine. Moreover, the varied and frequent joint-surfaces 
give rise to a number of fantastic peaks. At the mouth of 
Glen Sligachan we have the fine contrast of the pale dome 
of Glamaig and the uniform cone of Marsco, the granite 
mountains, on the left ; while on the right, above the fern 
and bogland, rise the black crags of Sgirr nan Gillean, 
where some of the huge saw-teeth of the gabbro actually 
overhang their base. As we ascend the four miles of the 
glen and cross the low watershed on the col, we approach 
what is absolutely the sternest and grandest scenery of the 
British Isles. The enormous wall of Blaven now rises verti- 
cally from a desolate hollow, its crest, 3040 feet above the 



A GRANITE HIGHLAND 211 

sea, cut by steep gullies in which snow may lie throughout 
the summer. Scarcely a ledge of grass can rest upon it, and 
the powdery taluses at its foot are themselves singularly 
steep. The blackness of the rock adds to its impressive 
wildness ; the granite masses are now left behind, and, as we 
climb a shoulder on the west, we look down on the hollow of 
Loch Coruisk. This narrow lake, almost at the sea-level, is 
nearly two miles long, and is surrounded by mountains rising 
some 3CXX) feet above it. Grass spreads freely over the 
lower slopes, but is seldom touched on by the sun. The 
general impression is one of loneliness and gloom, and the 
huge cliffs catch now and again long drifts of the Atlantic 
cloud. The great combe at the lake-head, the ** hollow of the 
waters," is bound by black crags which rival Blaven; but 
here they are massed together, leaving between them only 
the canon of a foaming stream. Beyond the grim wall on 
the west, another rises, still more pinnacled and precipitous ; 
and for a long time these ridges of the black Cuchullins were 
regarded as absolutely inaccessible. 

On the seaward side the valley opens into a broad fjord. 
Loch Scavaig, its barren gabbro walls repeating the features 
of Loch Coruisk. The horizontal scale of these landscapes 
is readily forgotten, and black crags fully four miles away 
seem to tower above us in this grim dark fastness of the 
rocks. It is a scene to be alone in for a time ; and then all 
the legends of the storm-gods may be realised, as the faint 
gleams of sunlight sweep across the lower slopes, and the 
cloud-wisps come and go above the desolate hollow of the 
lake. 

As we return to Sligachan, all the granite hills flush rose- 
red in the glow of evening, until they resemble the Pyramids 
in an Egyptian sunset ; but even now the Cuchullins remain 
dark and cold. To-morrow we can wander across their less 
frequented passes, where there is still a chance of startling 
an eagle in some hollow filled with the sea-mist. And we 
shall find that this igneous core, this cleft heart of a volcano, 
is at least as complex in its details as our open granite high- 
land. 

The Cuchullins are, indeed, seamed with dykes and veins 
of basalt and of fine-grained gabbro. Igneous activity clearly 
went on long after the intrusion of the main mass that now 
forms the mountains. The latter mass itself sends oS sheets 



212 OPEN-AIR STUDIES 

into the suiTounding basalts, and has in places a remarkable 
flow-structure and banding, which were set up when it was 
in a viscid state.^ 

It is not surprising that the constituents of a coarsely 
crystalline rock should be dragged out and arranged in a 
particular direction, as the mass gives its last movements 
prior to its consolidation. The edges of many granites show 
a streaky grouping of the constituents, particularly of the 
micas, the flow- structure being parallel to the plane of junc- 
tion of the granite and the surrounding rock. But it is 
more difficult to account for the occurrence of distinct bands 
of rock of different compositions, such as we may come across 
on the surfaces of exposed slabs in the field. 

In some cases the appearance of banded structure is 
due to one igneous rock having been penetrated by another. 
Such an invasion often remelts the older rock, and a mingling 
of the two occurs along the surfaces of junction ; but the 
second rock proceeds to work its way forward in a series of 
parallel sheets, aided by some previous structure in the mass 
into which it has intruded. Thus, south of Newcastle in 
County Down, a rock which may be described as a somewhat 
crystalline rhyolite has penetrated a massive dyke of fine- 
grained gabbro, and a banded structure has been set up 
parallel to the flow-planes of the original dyke. The gabbro 
has opened along these planes, and the invader has taken 
advantage of them. 

But in Skye it is thought that a separation of the molten 
rock into materials of differing composition had already taken 
place in the great caldron down below, and that an igneous 
mass already possessing a certain structure was thus intruded 
into the position where we now find it. In this upward 
movement the lumps, so to speak, of one variety of the rock 
pressed against those of other varieties, and the whole became 
squeezed out into parallel sheets.^ The chemical composition, 
and therefore the proportions of the resulting minerals, differ 
considerably in neighbouring bands ; one is thus found to be 
rich in labradorite, and has a silica percentage of 52.8, while 
another consists largely of augite, with a silica percentage of 
only 29.5. 



^**^^1> 



^ Sir A. Geikie and J. J. H. Teall, " On the Banded Stracture of some 
Tertiary Gabbros in the Inle of Skye," Quart, Joum. Oeol. Soc.j vol. 1 (1894), 
I. 645. ' Work quoted above, p. 653. 



A GRANITE HIGHLAND 21 3 

This brings us to the interesting consideration of the 
origin of the varieties of igneous rocks. As yet we are 
only on the threshold of this important subject, and we can 
do little more than state the problem. Are all igneous rocks, 
as known to us in the upper layers of the earth's crust, the 
products of chemical and physical separations from a uni- 
form molten mass below? Or are there distinct types of 
lava ready prepared in separate rock caldrons, which some- 
times open at distinct points on the surface, or sometimes, 
at successive periods, at the same point ? 

The same volcano may erupt rhyolites for many years, 
and then proceed to emit nothing but basalts. Has the 
caldron beneath it become filled by a new material from 
some other source, or are we now receiving the results of a 
separation which went on long ago in the melted mass 
beneath our feet ? 

In special localities we can actually observe, on the rocky 
surface formed by the exposed and denuded caldron, how a 
separation took place in the mass before it finally crystal- 
lised and cooled. We have already said that a granitic mass 
may be a true granite, with orthoclase, at one end, and a 
quartz -diorite, with plagioclase, at the other. Professor 
Vogt^ has studied an extreme case at Huk, near Chris- 
tiania, Norway, where a dyke, ten metres wide, consists of 
a porphyritic mica-syenite in the centre and a fine-grained 
mica-diorite, rich in magnetite, at the margins, the silica 
varying as we go outwards from 63 to 47 per cent., and the 
iron oxides from 3 to 12.5 per cent. At Ekersund in Norway, 
Vogt finds igneous rocks, well-developed diorites, consist- 
ing of labradorite, rhombic pyroxene, and titanic iron ore 
(an oxide of iron and titanium), in which the ore in places 
forms 80 per cent, of the rock ; and he believes these masses 
to have separated out from a uniform molten rock, the other 
extreme product of which is seen in the same district as a 
granite containing rhombic pyroxene. 

Messrs. Dakyns and Teall,^ in a paper of great interest, 
dealing with intrusive masses near the head of Loch Lomond, 
have suggested that rocks composed only of magnetite and 

^ See review by J. J. H. T[eall], Oeol. Mag., 1892, p. 84 ; and Teall, 
" The Sequence of Plutonic Rocks," Natural Science^ vol. i, p. 288. 

^ "The Plutonic Rocks of Garabal Hill and Meall Breac," Quart, Joum, 
Oeol, Soc., vol. xlviii, p. 118. 






^ 



214 OPEN-AIR STUDIES 

olivine, or of pure magnetite, may arise in igneons caldrons 
by extreme processes of separation. The area discnssed by 
these authors contains rocks varying from a type consisting 
of olivine and augite only, with a silica percentage of 38.6, 
to a fine-grained granite with siUca eqnal to 75.8 and potash 
to 6.5 per cent. The authors believe that the whole complex 
series has resulted from one original lava-basin. 

On the other hand, we are now ascertaining how the 
intrusion of an igneous rock into an older one often remelts 
the latter and allows of the most intricate and delicate inter- 
mingling of the materials of the two. Sometimes only some 
of the constituents of the invaded rock become melted ; and 
then the invader, in a liquid state, penetrates in between 
the remaining crystals, uniting with the remelted matter and 
finally crystallising as a new groundwork to the rock. Here 
we have a composite rock-mass produced, of a very puzzling 
character. Without careful study in the field, and a series 
of microscopic sections, we could not possibly work out its 
mode of origin. Occasionally the results are extremely de- 
ceptive, and give us serious warnings as to concluding rashly 
on the origin of porphyritic crystals. In one case^ a fine- 
grained but porphyritic granite has intruded into a large 
dyke of andesite. The glassy groundwork and the pyroxenes 
of the latter have partly melted, and the molten highly sili- 
cated rock has penetrated in among the small unmelted 
plagioclases. But the porphyritic crystals of quartz and 
orthoclase, which were already floating in the invading mass, 
have been carried into the yielding sponge-like substance of 
the partly melted andesite. When all has cooled again to- 
gether, the general eflFect of the new mixed rock is still that 
of a dark andesite ; but it has become stuck full of con- 
spicuous crystals of quartz and flesh-red orthoclase. 

The conclusion is that similar processes of admixture and 
interpenetration may go on on a large scale underground. 
Professor SoUas^ has argued that any separation of the 
material available for the manufacture of igneous rocks has 
already taken place during the consolidation of the earth's 
crust ; the remelting of one of these layers by local causes 

* G. A. J. Cole, '* On Derived Crystals in the Basaltic Andesite of Glas- 
dnimman Port," Trans. Hoy, Dublin Soc^ vol. v, p. 239. 

' " On the Volcanic District of Carlingford and Slieve Gullion, Part I.," 
Trans, Jtoy, Irish Acad,, vol. xxx (1894), p. 509. 



A GRANITE HIGHLAND 2 15 

would give us a well-marked type of rock in any lava-basin 
that might be established. The inflowing of material from 
another layer before the first was exhausted might produce 
a mixed rock of intermediate composition; or, if the new 
material entered after the first had been extruded in the 
form of lava, the character of the eruptions on the surface 
above the caldron might become abruptly changed. 

But we must not now attempt to follow out these some- 
what speculative trains of thought. We have at any rate 
seen the interest of any observations that we may make on the 
contact of one igneous rock with another, or on the occur- 
rence of different bands in the same dyke or intrusive mass. 
Day after day we may revisit our granite or our gabbro 
highland, and note the variety of its mineral characters from 
one end to the other. Dykes and seeming oflFshoots must be 
traced, if possible, to their parent mass. Lumps of other 
rocks that have been picked up by the invader must be 
studied, with a view to seeing if any have been partly or 
wholly absorbed; for such an absorption would naturally 
cause a local variation in the characters of the intrusive mass. 
And all day long in our researches our feet are wandering on 
the bare rock or the heather, or on the crisp short mountain- 
grass ; the clouds drive up the great valleys beneath us and 
creep across the wind-swept cols; and the crumbling tors 
upon the ridges seem dead and coldly crystalline, and are 
damp even at noonday with the penetrating mountain-dew. 
Yet before us rises, like a grim and fantastic vision, the 
picture of the seething and struggling of this ancient 
caldron, buried four or five miles underground ; and in the 
bared slabs of granite, seamed with dykes and veins, the 
earth has yielded up another of its secrets to us. 




CHAPTER Vm 

THE ASSALS OF THE EARTH 

We have hinted that the age of igneon? rocks can in some 
mea^nre be disoc*veTed bv examininsr their relations to the 
snrronDding strata. If ther intmde into the latter, their 
date mnst h^ later than that of the depc^tif»i of the strati- 
fied recks. If- however, the igneons mases are overlain by 
beds which contain pebbles worn from them, they mnst be 
distinctlv older than those beds. If. a^ain. tnf& and lavas 
lie among strata in regular layers, being thns. as we say, 
" interbedded " with them, the igneons series and the strata 
are of the same geological age. 

Bnt how shall we discover to what period of the history 
of the earth these stratified rocks belong ? How shall we 
divide up the long past ages of which we have no written 
records? 

It is clear that in anv limited district we mav be able to 
work ont the order of succession of the deposits. Where 
one group of strata is lying upon another, and where the 
rocks do not appear to have sufiFered from any great dis- 
turbance of the earth's crust (see Chapter X), it is obvious 
that the upper beds will be newer than the lower. When 
they lie, like courses of masonry in a fair building, evenly 
up^m one another, we say that they are ean/ormahle, and 
that they have been deposited steadily in the same great 
hollow of the crust ; probably this area was slowly sinking, 
and thus allowed room for each fresh stratum spread upon 
it. Where, however, one set of rocks has been uptilted and 
denuded, a second set being deposited across its worn-down 
edges, we say that we have an unconformable junction, or an 
unconformity (fig. 17). Every modem beach is thus un- 
conformable to the shore on which it is being laid down. 
In our walk along the shore (p. 95), we saw a junction of 
this kind, where sand and boulders were accumulating across 
^he rihH produced by the upturned edges of old strata. 

2l6 



THE ANNALS OF THE EARTH 217 

An unconformity may thus be visible at a glance in a 
quarry or in a cliff-section ; but in many cases it may be 
necessary to trace out the junction for some miles, the 
degree of tilting of the lower series of beds being but slight. 
However, the irregular and worn surface of that series will 
often be a guide; and a still surer piece of evidence will 
be furnished by the discovery of pebble-beds in the upper 
series, formed of materials derived from the lower series. 
It is obviously not necessary, in that case, that the contact 
between the two rocks should actually be visible at any 
point. If one rock contains pebbles worn from another, 
unconformity, whether local or far-reaching, is proved satis- 
factorily, though the true plane of junction may never be 
discovered. 

Unconformity commonly originates in the raising of strata 
until they come under the influence of ordinary agents of 
denudation. They thus form a local land-surface, while 
deposition goes on elsewhere. At some later time, submer- 
gence takes place, and strata are laid down in the excavated 
hollows of the hills, and finally even across their ridges. 
There has been, however, a marked interval between the 
two series, of which no record, beyond, perhaps, a few ter- 
restrial deposits, has been preserved. To fill up this gap, 
we must go elsewhere, to some region where elevation did 
not take place at the same time. Hence, could we know the 
whole world, we could compile a complete history from its 
stratified deposits, every local unconformity being represented 
by a conformity somewhere else. 

Occasionally, as the Challenger observers have found, 
even in water 1700 fathoms deep^ the soft but partly con- 
solidated sea-floor may be disturbed by currents and may 
become broken up, irregular lumps of the beds that were 
formed under conditions more favourable to deposition 
becoming rolled along and banked together, finally to be 
covered by a new stratum. This is a special case of uncon- 
formity, the cause of which has been a change in the direc- 
tion of currents, and not an upheaval of the sea-floor. In 
this way, in the " Carboniferous limestone " of County Dublin, 
lumps of a similar rock occur, evidently derived from the 
underlying beds of the same series ; remains of corals, sea- 

* See W. F. Hume, **The Genesis of the Chalk," Proc. Oed. Assoc.y vol. 
xiii, p. 231, 



2l8 OPEN-AIR STUDIES 

lilies, &c., may be found within the lumps, and other 
examples of the same species may have used these rolled 
blocks as a basis for their growth. In such a case the 
unconformity must be fairly local in character. The whole 
series of strata is, indeed, conformable, when judged by the 
regularity of its bedding ; and no long interval is represented 
by the phenomena of the blocks derived from earlier layers. 

Sometimes two or more unconformities may occur in a 
small space of country. Thus on the shore at Skerries, in 
the north of County Dublin, the sea has exposed a series of 
altered shales, which we will call A ; a limestone series, B ; 
a gravel series, C ; and it is also here and there depositing 
the present beach, D. The tilting of the beds A and B does 
not correspond, so that we suspect an unconformity, although 
the water covers the actual junction. The case is proved, 
however, by the occurrence of a magnificent old beach in the 
series B, formed of great flaky pebbles worn from A. A 
little farther south, certain beds of B have been churned up, 
as described on p. 217, giving us a second unconformity, but a 
purely local and trivial one. In the little cliff above, on the 
other hand, a very obvious unconformity is seen between B 
and the gravels C, the latter lying across the edges of the 
beds B, while the surface between has been ground down 
and striated by glacial action. contains scratched blocks 
derived from both B and A, together with a number of 
materials borne by ice and rivers from distant areas. Finally, 
the modem beach D is being formed from the decay of all 
the preceding deposits, and in places resembles, repeating 
the details with the most interesting accuracy, the very 
ancient beach exposed in contact with it on the surface of 
the series B. Thus in three hundred yards or so we have 
three principal unconformities, and one trifling one, the latter 
being due to local changes in the conditions under which the 
strata B were being deposited. 

In an unconformable junction, the lowest bed of the 
upper series crosses, as we have said, the worn-down edges 
of the lower series ; and this bed is said to successively over- 
step^ those beneath it, one after another (fig. 17). Again, 
in the basin-like hollow of a sea or lake, particularly if its 
floor is sinking, each successive stratum of the upper series 

^ See A. Jukes-Browne, to whom this term is due, " Handbook of Physical 
Geology/* 2nd edition, p. 548. 



THE ANNALS OF THE EARTH 219 

extends farther across the lower and unconformable series 
than does the stratum which lies immediately below it and 
in conformity with it. Thus the first stratum of the upper 
series occupies only a small area on the floor of the hollow ; 
the next, resting conformably on it, spreads more widely ; 
and this increase in the area of successive layers becomes 
the more marked, if the shore against which they are de- 
posited is a gently shelving one. If the coast drops down- 
ward, on the other hand, in a vertical wall, as in some 
Norwegian fjords, this difference between the layers is of 
course abolished. The spreading of any one layer of a con- 
formable series beyond the limits of the underlying layer or 
layers of the same series is spoken of as overlap (fig. 17). 




Fig. 17.— Unconpormablb Junction, with Overlap and Overstep. 

The series A-D is unconformable to the series 1-6, &c. D oversteps succes- 
sively I, 2, 3, &c. C overlaps D, and is overlapped by B, which is in turn 
overlapped by the youngest bed, A. 



Thus in any one district the relative ages of rocks, 
whether sedimentary or igneous, can be fairly made out, 
and we can even learn a good deal as to events which took 
place between the formation of one series and another. 
But what we want is to be able to go up to a rock-mass in 
any region, and to discover from its special characters the 
period at which it was constructed. It is improbable that 
we shall ever be able to do this in the case of igneous rocks, 
seeing that lavas and intrusive masses do not seem to have 
changed their nature from the time of the earliest eruptions 
until now ; and all attempts to classify such rocks accord- 
ing to their geological age have hopelessly broken down. 
Similarly, sandstones and clays and limestones seem to have 
existed in all times, and a limestone may be deposited in 
one part of a sea while a sandstone is being deposited simul- 



220 OPEN-AIR STUDIES 

taneoosly in another. Even the crystalline rocks called 
schists and gneisses (Chap. X) may belong to very different 
ages. 

Thus we say that, in the case of any rock, " lithological 
characters," i.e,, the nature and structure of the stone 
itself, are useless in assigning it to its place in the annals 
of the earth. We have now, however, another and a 
remarkable guide, which we can employ in any quarter of 
the globe. 

We are all acquainted with fossils (Plate X). By this 
term we now mean the remains of any plant or animal 
that are found included in a rock.^ We must use our 
discretion as to how far we should apply the word " fossil " 
to modem cases of entombment. A goat might become 
involved in a recent mud-flow on the flanks of a mountain ; 
the rootlets of living plants, again, penetrate a long way 
down into the crevices of rocks ; but neither of these cases 
gives rise to fossils in the generally accepted sense. Some 
fossil shells have preserved even their lustre, while Jbhe 
calcium carbonate of others has actually become changed, 
molecule by molecule, into some other chemical substance. 
Silica, iron carbonate, iron sulphide, and gypsum, are thus 
found actually replacing the original shells or hard parts 
of many organisms ; and silicified tree-stems are well known 
from many parts of the world. Very often, all that is left 
us is a cast, formed by the fine particles of the rock itself, 
which have penetrated the hollows of the shell or skeleton 
and have taken an accurate mould of them. Clay forms 
excellent internal casts, and the fine limestone-mud associated 
with shell-banks has a similar effect. Often the substance 
of the fossil itself has become dissolved away, after its en- 
tombment, and a hollow space has arisen ; but the envelop- 
ing and consolidated rock has at the same time taken an 
external cast of the fossil, from which many of its characters 
can be ascertained. Moreover, an internal cast may have 
been formed as well, which is generally fixed to the sur- 
rounding rock at the points where the material penetrated 
into the hollow of the shell In some cases, however, the 
solution of the shell leaves the internal cast to rattle loosely 

^ Up to the earlier years of the present century, a "fossil" meant 
anything dug up {fodio, fossum) out of the earth, and the objects to which 
the term is now restricted were called "organised fossils." 



THE ANNALS OF THE EARTH 22 1 

inside the external one, and to fall away when we break 
open the block of stone. 

Excellent internal casts can be seen in the rougher 
beds of Portland limestone, known as the "Roach bed." 
The objects called the "Portland screw" are the internal 
casts (fig. 1 8) of a long spiral gastropod shell, a Gerithium ; 
and casts of a bivalve mollusc, Trigonia, are also frequent. 
In the latter, the depressions where the muscles were 
attached to the shell are of course represented by raised 
oval patches, and the teeth of the hinge, which are beauti- 
fully ribbed with fine ridges, are recorded in reversed pat- 
tern on the cast. 

Casts are most common in sandstones, owing to the 
permeability of the material, and are 
frequently the only indications of fossils 
throughout the rock. In clays, on the 
other hand, even the most delicate fossils, 
such as foraminifera decorated with fine 
spines, are generally well preserved. 

Internal casts are often formed of 
marcasite, so that we have a mould of 
the fossil apparently modelled out of 
shining brass. These handsome speci- 
mens are unsatisfactory for collections, 
since so many, in the course of years, ^^^ ^g. - Internal 
go to pieces through decomposition of CastofaCbrithium, 
the iron sulphide (see p. 17). Portland Stone. 

Fossils, we should also note, often serve 
as a centre round which chemical substances present in the 
rock collect. Ooncretions are thus formed, which are com- 
monly harder than the rock itself, and which are seen sticking 
out on quarry-sections, or on cliffs, along the lines of bedding. 
At Whitby, for instance, where every visitor learns to be 
interested in geology, the concretions of calcium carbonate 
in the shales are pretty certain to reward the fossil-hunter. 
They can be broken open by the hammer along the bedding- 
planes that pass through them, and most frequently a 
perfect specimen of an ammonite is found lying, brown 
and lustrous, in the middle. 

While dealing with fossils, we may perhaps note how 
even the tracks and footprints of animals (p. 104) may be 
preserved by the gentle deposition of a stratum above that 




222 OPEN-AIR STUDIES 

in which the impressions were made. Similarly ripple- 
marks, water- groovings, sun- cracks, and rain -prints are 
often exquisitely "fossilised." Usually the footprints can 
be best studied on the under- surface of the covering bed, 
on which they stand out as casts. Worm-burrows, again, 
may be filled up by fresh sand, perhaps of a different colour 
to that in which the animals bored ; and such traces of 
worms are sometimes the only evidence left to show us 
that life existed in the area in which the beds were being 
laid down. 

Fossils must long ago have been observed by the 
primitive peoples of the earth, and may have been regarded, 
like meteorites, with a certain amount of reverence. Mr. 
Worthington Smith ^ records a case where the body of a 
girl, in a tumulus of the bronze-age near Dunstable, was 
found surrounded by 158 sea-urchins collected from the 
Chalk, more than half of which were perfect specimens. 
It is probable, then, that some mystery attached to these 
strangely shaped objects in the earth. 

The ancient Greeks recognised that fossils were the 
remains of creatures which once lived in the places where 
they now are found. They saw that, from one cause or 
another, land and sea had changed places, and that marine 
shells had often been left high and dry.^ It seemed, how- 
ever, difficult to conceive that a sufficient number of changes 
had gone on to account for the great variety of beds of 
rock crammed full with animal remains. Aristotle, in the 
fourth century B.C., thought to help on matters by suggesting 
that the earth itself contained a mysterious force within 
it, whereby animals grew in moist rocks, which subsequently 
consolidated and enclosed them. Such animals, we may 
presume, were like the toads that are sometimes found in 
hollow stones, living and breathing, but never seeing the 
world around them. We now know, however, that such 
toads have entered the hollows of the rocks in an infant 
form, and subsequently have grown to larger size. This 
idea of the development of animals in the earth itself spread 
very widely, and formed one of the chief errors that early 

1 Nature, vol. xliii (1891), p. 320. 

2 See Sir C. Lyell, "Principles of Geology," opening chapters; and O. 
C. Marsh, "History and Methods of Falsoontological Discovery," Nature, 
vol. XX, pp. 494 and 515. 



THE ANNALS OF THE EARTH 223 

geologists had to fight against. Even in the eighteenth cen- 
tury, opinion was greatly divided on this point ; and the teach- 
ings of Professor Beringer of Wtirzburg seem to have been 
in favour of the plastic force as recently as 1726. The 
solid globe was supposed to be like an Italian image-maker, 
continually turning out pattern after pattern and copy after 
copy, some of them like things in heaven or earth, and some 
of them entirely works of fiction. 

Professor Beringer went so far as to publish a book 
entitled " Idthographiae Wirceburgensis, ducentis lapidum 
figuratorum, a potion insectiformium, prodigiosis imaginibus 
exomatas specimen primum," in which he represented, on 
twenty-one small folio plates, some of the most extraordinary 
fossils ever discovered in his or in any other district. This 
work, which was guided and inspired by Beringer, appeared 
under the name of Hueber, a student of the University, for 
whom it served as a thesis for his Doctor's degree.^ The 
drawings include a variety of insects with extended wings, 
spiders with their webs, crustaceans and slugs, and a few 
respectable-looking shells. Vertebrates are represented by 
frogs, fishes, and (plate iv) the most grotesque birds, two 
of which have eggs lying beside them. Flowering plants 
are also figured ; but the greatest marvels are certain stones 
bearing carvings of the sun and moon, comets and stars, and 
finally even Hebrew letters (plate vii) in relief. These 
letters, including the name of Jehovah, were found occasion- 
ally on the surface of marine shells. One would have thought 
that such wonders would have raised suspicion in the minds 
of their discoverers ; but young Dr. Hueber defended them 
as being the work of Nature, and as being intended for the 
spiritual edification of his compatriots.^ 

Unfortunately, the whole series of specimens proved to 
be manufactured by a humorous ex-Jesuit named Rodrick 
(? Roderick), who was tutor to the children of one of 
Beringer's colleagues. This ingenious if unscrupulous man 
hired small boys to bring the "fossils" to the professor, 
asserting that they had found them in a neighbouring hill. 
When Beringer very properly wished to investigate matters 

* See Ph. X. Leschevin, " Notice sur Lithographia Wirceburgensis, et sur 
la mystification qui y a dound lieu," Magasin EncyelopMique, tome vi (1808), 
p. 116. 

2 ^' Lithographise Wirceburgensis, &c," p. 70. 



2 24 OPEN-AIR STUDIES 

on the spot, similar " figured stones " were buried ready for 
him to find. When Hueber's work appeared, the explana- 
tion of the fraud, and the apologies of its author, came too 
late to save Beringer from ridicule. He bought back as 
many copies of the book as he could procure ; but these and 
the remaining stock were somewhat cynically reissued, with 
the suppression of Hueber's preface and under Beringer's 
own name, after the death of the unfortunate but credulous 
professor. 

It is probable, however, that we all, like Beringer's ac- 
quaintances and pupils, have pulled out sufficiently remarkable 
fossils for ourselves from the solid rocks. If we go, for in- 
stance, to the vales of Derbyshire, we find whole blocks of lime- 
stone composed of shells. These stand out on the weathered 
surfaces ; and we also see numerous cylindrical bodies, with 
a hole down the centre, which are pieces of the stems of 
sea-lilies; and curving fragments of bivalve shells, which 
belong to a class known as the Brachiopoda ; and spirally 
coiled univalves, representing an early type of Gastropod. 
In a holiday in Dorsetshire, again, we may find looser yellow 
limestones and white chalk, in which the shells are still more 
beautifully preserved ; and in the Isle of Wight, particularly 
at Totlands Bay, there are clays and sands from which we 
can detach the fossils with our fingers. We may make col- 
lections at all these places, and may keep them in separate 
drawers when we go home. If we compare them carefully, 
we shall notice that the kinds of fossils from any one of 
these localities are not the same as those from either of the 
others ; after a little time, we might learn to mix them up, 
and to sort out those from the grey limestone of Derbyshire, 
the softer limestones of Dorsetshire, and the sands of Tot- 
lands Bay, by recollection of their special characters. 

But, if we go to the fine quarries above Cheltenham, we 
shall find many of the same fossils as occur in the yellow 
rocks of Dorset ; if we go to the flanks of the Mendip Hills, 
we shall find others agreeing with the shells of Derbyshire ; 
and hence we see that the same kinds of fossils occur in 
widely different districts. 

For purposes of recognition, geologists, like zoologists 
and botanists, have to give each distinct kind of plant or 
animal a name ; and these names have to be of such a char- 
acter that people in any civilised nation can make use of 



THE ANNALS OP THE EARTH 22 5 

them. By common consent, the classical languages, Greek 
and Latin, have been used as the foundation for such names ; 
and, until recently, Latin was the langnagc commonly used 
when any book was intended to be read in more than one 
Enropean conntry. Plants and animals are grouped, as we 
know, into gceat "classes," and then into "orders"; and 
then these are divided into " families." Each family contains 
one "genua," or a number of "genera," and each genus 
consists of one or more " species." When we wish to refer 
to a particular species, which has been described by some 
observer as distinct in one or more of its characters from all 
other species, we use the name of its genus, followed by that 
assigned by its discoverer to the species. For instance, there 




Fin. 19a.— Pecienficoi-m fio. 196.— Pecien cino(us(Ur- FiO. igc.—Pteten 

(CeDoiDanian stugo, Cro- gonian atOigo, Cretaceous ialandiout (Ra- 

taceouB period). period). cent period). 



is at present living a series of bivalve molluscs which are 
placed in the genus Pecten, a name referring to the comb- 
like markings or ribbings on their surface. Among these, 
sufficient differences have been observed to necessitate their 
grouping into more than a hundred species, such as Peclen 
maadmiis (the Scallop), Pecten nobilis, Peclen cpereularis, &c. 
(Compare figs. 1911, 19&, and 19c.) In each case, the second 
name is, as we say, " specifia" 

Hence we have to go with onr fossils to the zoologist or 
the botanist, before we can give them proper names. But 
again and again we find mat no living species is quite 
like our ancient specimen, and we learn that very many 
species have disappeared from the sarface of the earth, or 



226 OPEN-AIR STUDIES 

have become extinct. Thus there are aboat four times as 
many extinct species of Pecten as there are living ones. 
Moreover, a great number of our fossils cannot be fitted 
into any existing genus, and even many families and orders 
are only known from fossil specimens. Gould we continue 
to push our observations over the rocks of the whole of our 
islands, we should soon become convinced of the extensive 
changes that have taken place in the prevalent kinds of 
animals and plants since the dawn of life upon the globe. 
The assemblage of animals living in any district at the same 
time is called \\&fa%inaj the assemblage of plants being called 
its flora. We should find in time that whole faunas and 
floras of past ages had become entirely extinct. 

The fossil fauna of the Derbyshire limestone occurs, as we 
have seen, in parts of the Mendip Hills ; that of part of the 
Dorset coast is repeated in the Cotteswolds. It was reserved 
for a hard-working and observant land-surveyor to piece 
together such facts as these, and to read from them for the 
first time the annals of life upon the globe. 

William Smith was bom in western Oxfordshire in 
1769,^ high up on the plateau of the Cotteswold Hills, and 
must have been familiar from his childhood with a rich 
variety of fossils, which roll out into the roadways from the 
limestone cuttings, and which are even used for making 
the roads themselves. Brachiopods and lamellibranchs and 
cephalopods, well preserved starfish and sea-urchins, must 
have convinced him very early of the former extensions of 
the sea ; and we may picture him wandering down the steep 
lanes to some particular quarry for one kind of fossil, and 
across the windy fields upon the ridges for some other of 
which he knew the exact locality. 

We know, at any rate, that at about the age of twenty- 
one Smith had discovered that fossil faunas succeeded one 
another in regular order. Certain assemblages of fossil 
species were always, as he showed, to be found underlying 
other distinct assemblages ; in other words, strata covM he 
identified by the fossil faunas that they contained. 

Thus, in section after section, he observed that one set of 
fossils, which we will call A, was followed, as he went up- 
wards in the series of strata, by a set that we will call B, and 
this by a set C, and this by a set D. The order was con- 

1 John PhiUips, ''Memoirs of V^illiam Smith, LL.D./' 1844. 



THE ANNALS OF THE EARTH 227 

stant. Even if, from some local cause, B was missiDg, C 
would be found resting upon A. After gathering a large 
amount of evidence, William Smith found that the occur- 
rence of fauna C, for instance, would enable him to predict 
that fauna B or fauna A lay somewhere down below. Hence 
the past history of life upon the globe was marked by a 
succession of faunas, and the observation of any one of these 
by itself would enable us to say that the rocks containing it 
were made at such and such a period of that history. 

In this way the annals of the earth were laboriously 
compiled. William Smith extended his experiences, while 
working as a civil engineer on the Somerset Coal Canal ; 
whether lodging in some country-inn, as at Dunkerton, or in 
his own house at Midford, he became thoroughly acquainted 
with the fossilif erous strata around Bath. In those days, the 
modes of travelling encouraged observation of the country. 
Hills and valleys were important features to the post-chaise 
or the coach, just as they are to the modern cyclist. The 
traveller could look far ahead, without, as now, the risk of 
receiving coal-dust in his eye or of having his head taken ofiE 
by a bridge-pier ; and the colour of the cuttings or of the 
distant quarries could be traced from ridge to ridge across 
the landscape. In leisurely driving, hills might be walked, 
and rocks might be examined along the roadside ; and quaint 
local specimens could sometimes be picked up on the chimney- 
pieces of wayside-inns. In traverse after traverse of England, 
Smith assured himself of the truth of his doctrine of regular 
succession ; and he gave names, as Professor Werner had 
done in Saxony, to the several sets of strata that he came 
across. In 1 800 he made a memorable journey, on behalf of 
Mr. Coke, to Holkham in Norfolk, where he busied himself in 
resisting the inroads of the sea by constructing protective 
banks. We can picture his keenness as he ascended the 
great plateau of the Cotteswolds above Bath, crossing his 
"Under Oolyte" and *' Great Oolyte" limestones, and as he 
traced out his well-marked divisions into the district of the 
" Oak Tree Clay " near Oxford. The long ridge of ** Green 
Sand" and "Chalk," capped by its dry plains,^ lay upon 
his right; and finally these also had to be surmounted as 
Cambridge was approached. Still moving north-eastward, he 

^ William Smith, *' Memoir to the Map Etnd Delineation of the Strata of 
England and Wales" (181 5), p. 42. 



228 OPEX-AIR STUDIES 

came across the barren heafchs of SofFoLk and Norfolk, wliere 
the decay of thrr Chalk strata has covered the coantiy with 
angular dints and sand, giving rise to what Smith calls ^ the 
gr^est breadths of pi:>Terty and wretchedness^*' Doabtlees 
his wheels sank into the loose and almost abandc»ied roads^ 
which are hardly likely to have been better than the tracks 
of west Suffolk in our own time. And finally he came over 
the rim of the Chalk again, and saw the modem ssaadj 
reaches stretching at the foot of Uolkham woods^ and the 
cold line of the North Sea breaking on them, and arranging 
new strata on the shore. A journey of this kind was to him 
full of a sober joy, and he went forward map in hand, with 
the scheme for a " delineation " of our strata already in his 
active mind. 

Naturally, he made some mistakes as to the order of 
superpoation of certain beds. Where a set of strata appeared 
to him resting on another set below, he might easily have 
overiooked some unconformity that had occurred, and have 
placed the two in direct succession. The beds that properly 
filled the gap might be discovered elsewhere, and might come 
to be placed in his classification above those with which he 
had first become acquainted. But in time he produced a 
convincing work, illustrated by Sowerby, entitled '"Strata 
Identified by Organised Fossils," of which four parts alone 
were issued. These are now rarely met with, but they 
effected their purpose in a very few years. About the same ' 
time (1815), Smith received Government assistance towards 
the ccmstruction of his great map of England and Wales^ on 
which his principles of the classification of strata were dis- 
played. The areas occupied by the various divisions of the 
strata were coloured with washes bearing some resemblance 
to the colours of the actual beds — a plan that has ever since 
been adopted by the surveys of the British Isles. 

Thus the great discovery, first circulated by Smith in 
manuscript in 1799, became open for the approval and ciiti> 
dsm of all. The foundation of what we now call strati- 
graphical geclofjy was firmly laid by this busy professional 
mao, who, but for his open-air studies, might easily have 
remained merely a successful civil engineer. 

Smith chose the names of his series of strata mostly on 
account of their local peculiarities, or from terms used by 
qnarrymen and farmers. Sometimes a district gave its name 



THE ANNALS OF THE EARTH 229 

to a series, and this plan has since been widely followed. 
No uniformity is discoverable, however, in the names em- 
ployed by any geological survey ; and many of our British 
terms have become translated and adopted by every foreign 
country. Of late years, an agreement with regard to some 
points has been arrived at, for mutual convenience, by means 
of the International Geological Congress ; and the following 
terms have been put forward for divisions of stratified rocks 
and for the periods of time occupied in their formation. 

The largest divisions of strata are styled, on this con- 
ventional plan, Growps, These are divided into Systems, and 
each system is divided into Series. These again are formed 
of Stages, The time-divisions corresponding to these are as 
follows : — 

Stratigraphical Divisions. Time-Divisions. 

GROUP. ERA. 

Systkm. Period. 

Series. E'poch. 

Stage. Age. 

It must not be supposed, however, that each stage, or 
series, or system, or group, took the same time to accumu- 
late as any other stage, series, &c. The extent to which, 
from our studies in the field, we agree to subdivide any 
particular division of the stratified rocks depends greatly 
upon our detailed knowledge of it ; and thus the stages of 
the later groups, the beds of which are so much the most 
convenient to study, represent briefer " ages " than many of 
the older ones. A whole system, moreover, may sometimes 
be established in a country where two unconformities, one 
above and one below, cut it off sharply from the other systems ; 
but subsequent research may show that in some other country 
this system is so closely and continuously connected with the 
one above or the one below that it would not have been 
worth while to distinguish it by a separate name, had obser- 
vation commenced in that particular area. 

The one principle of classification on which we now rely 
is that fossil faunas are to be our guide, and not the litho- 
logical character (p. 220) of the beds in which they lie. The 
fauna of one district may have spread only slowly to another, 
so that strata containing the same fauna were not necessarily 
deposited at exactly the same time ; but this will not affect 



2 30 OPEN- AIR STUDIR^ 

US in assigniog '^ ages " to the beds of aoy particular area. 
Species, moreover, varied, as they do now, from point to 
point, and we must thus, in our classification, regard the 
general aspect of a fauna rather than its minutest details. 
Some genera, and even species, have managed to persist 
through such a long succession of periods that they are of 
no value in classifying strata; others arose and vanished 
away in so short a time that they mark out "ages" very 
precisely. Where a fossil species occurs abundantly along 
a particular bed or set of beds, being restricted to it, or 
being only poorly represented above and below, we say that 
it marks a zone. We can thus speak of "the zone of Adino- 
camax plemis " (see Chapter IX), or " the zone of Pentamerus 
ohlongitsy 

By common consent, marine types of life have been used 
as the most convenient means of classifying strata. Fossils 
are rare in fresh-water deposits, and terrestrial deposits are 
very seldom preserved. A good deal of our knowledge of 
the land-animals of the past is, indeed, derived from the 
fact that their remains have been washed down into the 
strata which were forming on the shore. Marine beds, on the 
other hand, quickly and securely entomb any dead shells and 
bones that become mingled with them, while the abundance 
of life in the sea gives us plenty of material by which we can 
judge the character of the fauna. 

In the later chapters of this book, we shall have frequent 
occasion to speak of the "systems" established by geologists ; 
and their names, thanks to the writers of jwpular works and 
guide-books, are beginning to be fairly familiar as house- 
hold words. Considering what vast eras are covered by the 
annals of the earth, as written in its fossil faunas, it is im- 
portant to have some means of referring to particular periods. 
I am afraid, then, that the following table should be com- 
mitted to memory ; it is not more difficult than the lists of 
kings which we have to deal with in our studies of human 
history, and it represents a series of facts of vastly wider 
meaning, facts which, indeed, form the foundation of the 
history of every nation in the world. 




THE ANNALS OF THE EARTH 23 I 



Table of Stratified Eocks. 

Groups. Systems. 

(5. Post-Pliocene and Recent. 

4. Pliocene. 

3. Miocene. 

2. Oligocene. 

I. Eocene. 



in. Mesozoic 
or 
Secondary. 



n. Paleozoic 
or 
Primary. 



L ARCHiEAN. 



3, Cretaceous. 

2. Jurassic. 

1. Triassic. 

6. Permian. 

5. Garboniferoua, 

4. Devonian. 

3. Silurian. 

2. Ordovidan. 
^i. Gamhrian. 



I. The ARCHiEAN era^ is represented by so few fossils 
that no division into systems can be made. But probably 
it covers as long a series of periods in the history of life 
upon the globe as all the other eras put together. Worms 
and radiolarians are, however, almost the only living things 
that have left their traces. The oldest rocks of the Archaean 
group may, of course, represent periods before life actually 
existed. They consist of completely crystalline masses, like 
granites, together with others, which we shall learn to call 
" schists," and which may prove to be highly altered sedi- 
ments or crushed and drawn-out igneous rocks. 

The beautiful ridge of Malvern, which stands up like a 
blue wave against the sunset, sharply defined above the land 
of level orchards round it, is now known to be the relic of 
an Archaean mountain-range. It must have been several 
times buried in the sea, only to reassert itself as the most 
striking landmark of our Midlands. 

The long desolate islands of the Outer Hebrides are 

' For local guidance as to the areas in which the several groups and 
systems are exposed, see the maps and memoirs of the Geological Surveys of 
Great Britain and Ireland; H. B. Woodward, "Geology of England and 
Wales ;" Hull, " Physical Geology and Geography of Ireland ; " Kinahan, 
" Geology of Ireland ; " and Sir A. Geikie, ** Scenery and Geology of 
Scotland." 



232 OPEN-AIR STUDIES 

formed entirely of Archaean rocks, which appear also on 
the opposite mainland as a floor on which later mountains 
have been reared. The wild and weather-worn surface of 
Scandinavia probably offers us the largest European area 
over which Archaean masses are exposed; and the similar 
rocks of Scotland and north-west Ireland may be regarded as 
a continuation from Norway along the edge of the conti- 
nental plateau (compare p. 1 19). 

n. The Paleozoic era is that of " ancient life." Even 
at the base of the group, there is a great variety of fossil 
forms, which justifies us in searching diligently among the 
Archaean rocks for still earlier types of life. 

The Oambrian period has probably now been most 
successfully studied in Bohemia and in the north-eastern 
states of America ; but it derives its name from the Roman 
name for Wales. The black shaly beds on the moors north 
of Dolgelley, particularly in the boggy hollows north of 
Rhobell-fawr, contain numerous Cambrian fossils, which are 
best seen when the surface of a specimen is held obliquely 
to the light. 

The Ordovician period takes its name from the Ordo- 
vices, a tribe that formerly inhabited North Wales. On very 
many maps, and in many text-books, the older name " Lower 
Silurian " is retained ; but this term became objectionable, 
owing to the same rocks being styled by many authors 
" Upper Cambrian." The use of " Ordovician," as suggested 
by Professor Lapworth, prevents any further controversy 
about words. Snowdon is formed of tufifs and lavas ejected 
in Ordovician times; and brachiopod shells occur in the 
shales upon its very summit. 

The Silurian period is named after the Silures, who in- 
habited South Wales and the adjacent Marches. The whole 
of its stages are beautifully seen around the town of Ludlow, 
and fossils are simply abundant in the shales and limestonea 
A small patch of Silurian limestone at the Wren's Nest, 
near Dudley, has proved the most famous British collecting- 
ground ; but in Bohemia, and the island of Gotland in the 
Baltic, the fossils are still more richly preserved. The hand- 
some ridge of Wenlock Edge, sloping away eastward on the 
Bridgenorth side, and dropping steeply towards Church 
Stretton and Shrewsbury, is capped by the highest Silurian 
/siales; the great scarp, through which the road-cuttings 



THE ANNALS OF THE EARTH 233 

have been made, is formed of Middle Silurian limestones ; 
and the long and gentler slope below has the earliest 
Silurians at its base. We must remember that, before the 
introduction of the term Ordovician, most writers called the 
whole of our Silurian system " Upper Silurian." 

The Devonian system is mainly represented by fresh- 
water sandstones in the British Isles, and its marine type 
is best observed in Belgium. Devon itself, however, con- 
tains a complete series of marine strata, the "Plymouth 
Marble " being notable among them. This delicately tinted 
rock makes the buildings and walls of Plymouth glorious 
after a dash of rain, the pink veins of calcite shining then 
across the grey masses of the limestone. Bent and injured 
fossils are commonly seen on polished surfaces of this rock, 
and corals are particularly abundant. 

The sandstones formed in the great lakes of the period 
come up in the centre of the Mendip Hills, but are far more 
finely seen in the Breconshire Beacons away west. The 
roadside cuttings in Herefordshire constantly expose these 
beds, and they cover large areas in Scotland. 

The Oarboniferous system gets its name from the im- 
mense amount of coal that occurs amid its higher beds. 
Plant - life seems to have flourished with extraordinary 
abundance, and the forest-deposits and drifted snag-banks 
accumulated to form the most important industrial strata of 
the world. These deposits are, of course, terrestrial and 
estuarine, but in many areas the lower series are marine. 
In Scotland, however, the whole Oarboniferous system is 
estuarine, while in India it is marine throughout. 

The lowest Carboniferous series includes great beds of 
limestone, which are well known in Derbyshire and in the 
west of Yorkshire, and which are crowded with marine fossils. 
These strata weather out in huge steps across the landscape, 
giving a terraced character to the hills. In Ireland, similar 
features are noticeable in the west, while the central plain is 
formed also of Carboniferous limestone. Its hollows are 
occupied by broad lakes, with gently sloping shores; and 
every here and there the general level is broken by some 
ridge of Ordovician strata, the weathered-ont crest of an 
island round which the Oarboniferous sea once flowed. 

In England, great sandy beaches usher in the estuarine 
and terrestrial series, and the true " Ooal-Measures " are at 



234 OPEX-AIR 55TrDIES 

the top of th** syat»»m. The Forest of Dean forms an intereet- 
ing tableland, with the whole system expoeed open its flanks. 
On all sides we climb ap from the sandstones of the Devonian 
lake, across the Carboniferous Limestone and the central 
grits, to the capping of shales and coal-seams. The mines 
are hidden away in a tangle of old woodland, through which 
the footpaths wander, jnst as they may have done in the days 
of Caractacas and Cymbeline. It is a corioos high region, 
still cat off, as it were, from modem Britain. 

Bnt the central ** coalfields" of England are crowded with 
grimy villages, while the f nme of their chimneys blackens the 
air over thousands of sc(nare miles. At night the sky is ablaze 
with the flare of iron-fumaces, while red-hot flows of slag 
ran down the heaps like lava-streams. And then suddenly 
we leave this bnsy country, with its encroaching spoil-banks 
and its blackened stems of trees, for a land of green fields 
and apple-orchards white with blossom, of half-timber farms 
and churches with scjuare Tudor towers — and we know that 
we have passed beyond the Coal-Measures to some innocent 
overlying or underlying series. 

In the north of England, the coals are often worked in 
hollows between folds of unproductive moorland; and the 
great grits and limestones of the Pennine Chain rise up thus 
to form a pure mountain-area between the gloomy coalfields 
of Lancashire and west Yorkshire. 

The Permian system is insignificantly developed in Eng- 
land, and is only in part marine. In the south it is represented 
by red beds of conglomerate, containing many angular frag- 
ments, such as may easily have accumulated on a land- 
surface. These strata form the well-known red coast round 
about the mouth of the river Exe, and extending away to 
Teignmouth and Torquay. The system was named from 
Perm in Russia; but in most places it is convenient to 
regard it as a mere continuation of the Carboniferous. 

This sixth system concludes the Palaeozoic group. The 
faunas are throughout markedly different to those of the 
present day. It is important to note that in the Cambrian 
beds the highest forms of life known to us, the lords, indeed, 
of the Cambrian world, are the Trilobites (fig. 20), which were 
comparatively small marine creatures allied both to the scor- 
pions and to the humbler orders of crustaceans. The earliest 
known fishes are Ordovician or even Silurian, and for a long 



THE ANNALS OF THE EARTH 



235 



time they were held in check by " sea-scorpions " some fonr 
feet long. In the Carboniferous period, however, the fishes 
had asserted themselves, and a few amphibian remains have 
also been discovered. A great variety of shell-fish existed, 
but the proportions of the several classes were very different 
to what they are in existing seas. Thns in the Lower Oar- 
boniferons Limestone of Ireland we find that, out of 345 
species of shell-bearing animals, 37.5 per cent, are brachio- 
pods, 21,9 per cent, lamellibranchs, and 18.1 per cent, gas- 
tropods. Ont of 527 species recorded from modem British 




5 nnd 8 are fragmentaiy. 



seas, we havei — Brachiopods 1.3 per cent., lamellibranchs 
32,6, and shell-bearing gastropods 48.' 

Not only the species, bat most of the Carboniferons 
genera are now extinct. If we examine the plants, we find 
that forms now lowly and insignificant were then as lai^e as 
forest-trees. They had no rivals in the form of complex 
flowering plants, and their simple and seemingly wasteful 
methods of reproduction probably accounted for the rapid 
spread and growth of forests across eveiy continent. 

In Permian times, reptiles began to appear, and became 

' G. Cole. " County Dublin, Paat and Preient," Jrlik l/atamlUl, vol. i, 



2 7,6 OPEV-AIR STTDIE? 

predominant in the Mesozoic era. Thns eren as late as the 
clo«^ of the long PaUeozoic era, or probably more than half- 
way through the history of life n]x>n the globe, it was a 
straggle between reptiles and amphibians as to which should 
possess the empire of the world. 

IIL The Mesozoic or " middle-life " era opens with the 
Triassic period. This name is derived from the threefold 
di\nsion of the strata in central Enrope, where we have a 
fresh-water or terrestrial series above and below, with a 
marine invasion in the middle. A second marine series is 
now. however, included at the summit of the svstem. The 
Trias is marine thronghoat in Tyrol and soath-eastem Europe. 
In onr islands it is fresh- water or terrestrial (with the excep- 
tion of the very highest series), giving us useful beds of salt 
and gypsum, derived from the evaporation of lakes in a dry 
climate. The soft current-bedded sandstones, pale pink and 
red, and the red clays, that cover so much of England from 
Chester to the base of the Cotteswolds, belong to the Triassic 
system, and rest on Carboniferous and older rocks in striking 
unconformity. At the top, as may be seen near Bristol and 
in Countv Antrim, we have the return of the sea recorded 
for us, and marine molluscs occur plentifully in white marls 
and shales. 

The Jnrassic system is named from its excellent develop- 
ment in the Jura Mountains ; but its stages are usually named 
after English localities, thanks to the start obtained by the 
stratigraphical geologists of onr own islands. We have three 
series, the lower of which corresponds to the old British 
" Liassic " system, the middle and upper series representing 
what was called the " Oolitic " svstem. The Lower Jurassic 
series forms the undulating lowland that stretches for 250 
miles along the base of the Cotteswold Hills and their pro- 
longations ; it is set with clay-pits and occasional limestone 
quarries, both forming good hunting-grounds for fossils, which 
are often found replaced by marcasite in the clays. A large 
part of the face of the Cotteswolds is also formed by Lower 
Jnrassic beds, while the steeper crest and the plateau, the home 
of William Smith, consist of Middle and Upper Jurassic 
limestones, with considerable masses of clay. Oolitic beds 
(p. 1 10) are very common, and corals of modem aspect form 
broad banks and reefs. 

The soft oolite known as " Bath Stone " belongs to the 



THE ANNALS OF THE EARTH 237 

Middle Jurassic series, and to the Bathonian stage ; the still 
more famous building-stone from Portland is Upper Jurassic, 
and even French authors speak of the tltage portlaiidien in 
its honour. 

The close of the period was marked in England by 
estuarine conditions, which gave us the Purbeck beds of 
Dorsetshire and Sussex. 

The Cretaceous system will be dealt with in some detail 
in the next chapter, when we apply our mode of reading the 
annals of the earth to one especial district. It takes its name 
from the Latin creta, " chalk," ^ since that soft white lime- 
stone is conspicuous in the upper series. The Chalk, indeed, 
spreads across England from the coast of Dorset to Cromer, 
and extends beyond the Wash to Flamborough Head. It 
forms a broad and rolling country, the very type of which is 
to be found in Salisbury Plain ; its surface is bare, but for a 
few tree-clumps, and everywhere shows flecks of dry white 
rubble through the thin coating of brown soil. The white 
cliffs of Albion are a noble feature of our Channel coast, and 
are boldly repeated across the water by the similar masses at 
Dieppe. 

And with the Chalk the Mesozoic era also closed. At its 
outset, we find a mingling of extinct and modern types of 
life. The Trias contains molluscan genera from Carboni- 
ferous and Permian times, side by side with others that are 
still living and prolific. The great group of cephalopods 
known as "ammonites" (fig. 25), with their coiled shells, 
and with greatly folded partitions between their internal 
chambers, commenced in the Permian of India and spread 
rapidly in the Trias. Some molluscan genera which are re- 
stricted in area and in number of individuals at the present 
day flourished abundantly in early Mesozoic epochs — for 
example, Trigonia among lamellibranchs and Pleurotomaria 
among gastropods. The most marked difference between 
Mesozoic times and our own lay in reality in the character 
of the vertebrates. The fishes had laid aside much of the 
bony armour that characterised them up to Permo-Carboni- 
f erous times ; but the modem type of fish, with a fully de- 
veloped internal bony skeleton, did not appear in force until 
the Cretaceous. Mammals came in, in a very humble way, in 

^ Creta was a white earth from Crete, an early example of a locality giving 
its name to a rock-specieB. 



238 OPEX-AIR ^TTDIE? 

the Triaeeic period, and remained strange to say. extremely 
subordinate, and o£ the Lowest type:?, antil the close of the 
era. The real lords of the Mesozoic earth were the repdles^ 
of which we shall see a«:mething in our researches among the 
Surrey Hills. These predominant animals were fairly high 
np in the scale of Life, bat were not remarkable for their 
brain-power. A few «|iiaint birds hare also been traced ; so 
that all the great modem classes of life were represented. 

The Mesozoic plants remained for a long time of lowly 
character; bat a somewhat rapid change set in abont the 
middle of the Cretaceoas period. The tiowering plants and 
modem trees then began quickly to replace the old conifers 
and tree-ferns, and for the first time wild-dowers added their 
colours to the landscape. Marked as was the advance in 
life-forms, if we compare the highest Cretaceoas stage with 
the highest Permian, there were many changes still in store 
at the dawn of the Cainoosoic era. 

IV. The Caixozoic or " recent life " era is the only one 
that is divided upon a uniform and systematic plan. Sir 
C. Lyell, in 1833,^ proposed a series of names based on the 
number of moUuscan species which occurred both in the 
Cainozoic systems and in a living state in existing seas. He 
thus gave us a Pliocene system [trXeimv and koivw;, ^' more 
recent "J, in the upper beds of which 95 per cent, of the 
molluscan species are also found living, while in the lower 
beds the proportion is 35 per cent. Below this comes the 
MifjctM (jJLeUdv and icaivo^, '* less recent "), with some 17 per 
cent, of living molluscan species; and at the base is the 
Eocene (^ci? and icaivo% " dawn of the recent "), with 3^ per 
cent, of living molluscan species. The German geologist 
Beyrich showed later the necessity for introducing a fourth 
system, the Oligocene, or " little recent," between the Eocene 
and the Miocene. 

The whole of these four systems can be far better 
studied on the European continent than in their poor 
representatives in our own islands. LyeU, indeed, formed 
his classification after travelling in Italy and France, and 
with the help of the splendid collections then being made 
by French conchologists. 

The Eocene system of the Paris Basin is, however, 
fairly repeated in the south-east of England, especially in 

1 " Principles of Geology,** voL iii, p. 53. 



THE ANNALS OF THE EARTH 239 

the Isle of Wight and Hampshire. The black-blue clays 
of the pits immediately round London provide us with a 
fair number of fossils, and there are hard beds formed by 
estuarine shells in the sands about Chislehurst and Croydon. 
As a whole, our Eocene strata are soft and yielding, and 
produce only rounded hills, the slopes of which are liable 
to earth-slips after heavy rains. 

In the Inner Hebrides and north-eastern Ireland (p. 183), 
great volcanic eruptions broke out during Eocene times, 
the remains of plants that were growing on the land- 
surface becoming entombed amid the tuffs and lavas. 

The Oligocene system is largely represented by fresh- 
water beds in Europe, with evidences of frequent incursions 
of the sea in the south-east and east. Professor Judd has 
shown how the beautiful series of strata that occupies all 
the northern half of the Isle of Wight is the equivalent of 
the Lower Oligocene of the Paris basin. The shells are 
estuarine, fresh -water, and even terrestrial, with a few 
marine bands, and the soft clays and sands make collecting 
fairly easy. The state of preservation and the distinctly 
modern type of these fossils give even the most casual ob- 
server some idea of the "Cainozoic" character of the deposits. 

The Upper Oligocene is absent from our islands, as 
also is the whole of the Miocene system. The latter can 
be well studied in its three great marine series in North 
Italy and Austria, and in its fresh-water representatives, 
with a marine middle series, in Switzerland and France. 
The plant-beds of the British Isles, formerly regarded as 
Miocene, have now been referred back to the Eocene. 

The Pliocene sea has, however, left its traces with us, 
notably in the east of Norfolk and Suffolk. Here, in sandy 
excavations, we may see, as it were, sections of some modem 
shelly beach (Plate X). It seems hard to believe that half 
the species of molluscs, which we can so easily extract 
from their soft matrix, have become extinct since the 
formation of many of these loose and current-bedded de- 
posits. As we reach the higher series, this modem aspect 
becomes more and more striking, until we pass into the 
most recent geological formations, the " raised beaches " of 
the Post-Pliocene period. 

A great epoch of colder climate, with a remarkable 
development of glaciers, and of floating ice in European 



240 UPEX-AIR STl'DlRj 

waterFs. ixrt ill at the cloce of the Pliocene period, and gave 
Us oar wid^^-spivad " drifts,"* with their glaciated stones 
and thrir thick irregular beds of clay and sand. The later 
epochs o! the Post- Pliocene pass into historic times^ and the 
whole period corresponds with the existence of man opon 
the earth. 

The opening of Cainozoic times showed at once the 
prcrdomiuance of mammals. The hamble cneatores of the 
Merozoic era now assumed an immense superiority and 
variety. Like the Permian and Triassic reptiles^ they were 
adapted to a great range of food and habits, and some 
b^rcame specialised as vegetable - feeders, some as flesh- 
eaters ; some took to the sea, in the form of great toothed 
whales, while others, as little bats, flew in the air. The 
reptiles with equal rapidity became narrowed down to their 
present restricted types; their empire had been utterly 
taken from them. 

The older Cainozoic mammals were, however, widely 
different from any that we possess at the present day, and 
often combined the characters of two or more living genera. 
The humbler forms of life, however, such as the moUoscs, 
clos^.'ly resembled oar modern types, and lamellibranchs and 
gastropods were in Eocene times already largely in excess 
of brachiopods. The ammonites, so essentially characteristic 
of the Mesozoic periods, had entirely disappeared, though 
their ancient ally, Xautilus, still existed. The plant-life 
also approximated to that of our own times, and honey- 
sacking insects are consequently found as fossils in Cainozoic 
strata. 

The wonderful mammalian deposits of Provence and 
Greece,^ and of the Siwalik Hills in India, show us how, 
even in Pliocene times, the highest forms of life were still 
strangely distinct from those of the Post - Pliocene and 
liecent period. The types that we now know were then 
represented by more gigantic forms, which waged war upon 
one another, antil Man appeared among them. Here they 
met a creatare capable of killing off the fiercest of them 
by superior art and cunning, and of leading the more docile 
into perpetual and even hereditary slavery. The exact 
period of Man's entry upon the earth may never become 

* For a charming account of Cainozoic nianimalH, see Gandry, **Iie8 
ADCbtres de no« auimaux." 



THE ANNALS OF THE EARTH 24 1 

precisely known ; but Dr. Noetling has recently found some 
chipped flint flakes in Burma beneath 4620 feet of Pliocene 
strata, which contain numerous characteristic extinct mam- 
mals ; the instruments are thus at any rate of Lower Pliocene 
age.i 

In any case, the base of the Pliocene is vastly nearer to us 
than the Cretaceous, while the commencement of the Palaeo- 
zoic era lies some fifty times as far behind us. Estimates 
may be made, from the thickness of the marine strata com- 
posing the successive systems, as to the relative time that 
elapsed during their accumulation. To convert these data 
into actual years seems beyond our present powers, though 
several calculations have been made, based upon the rate of 
accumulation near existing shores. Giving the Cainozoic era 
its fullest value, as displayed to us by the Italian deposits, 
we may allow it to have equalled the Mesozoic era ; while the 
Palaeozoic era was fully four times as long as either. If we start 
our annals at the base of the Cambrian, with a time-point which 
we will call o, and divide a column representing subsequent 
time into 100 divisions, like the degrees on a thermometer, 
we arrive at the following approximate results : — 

(i) The Palaeozoic era extended from o to 68 degrees of 
our scale. 

(ii) The Mesozoic era terminated at 84 degrees. 

(iii) The Cainozoic era extended over the remaining 16 
degrees. 

(iv) In t£is comparatively short time of 16 degrees, as we 
shall see for ourselves when we come to our final 
observations (Chapter X), the most extraordinary 
changes went on in the surface-features of the 
globe, side by side with marked changes in the 
forms of mammalian life. 

(v) The oldest remains of man are found at 98 degrees of 
our time-scale, or two units only from its summit; 
while human " history," in the ordinary sense, even 
that of the Chaldaeans and the Chinese, can only be 
represented by a minute fraction of a degree. 

^ Noetling, "On the Occurrence of Chipped (?) Flints in the Upper 
Miocene of Burma," Records Oeol. Stvrvey of India, vol. xxvii (1894), p. loi ; 
and W. T. Blanford, " The Burmese Chipped Flints Pliocene, not Miocene," 
Nature, vol. li (1895), p. 608. 



242 OPEX-AIR fnrOIES 

Here we are met. then, by the most remarkable and 
inspiring feature in the whole annals of the earth. Man, 
with all his pride of life and reason, is still, as it were, only 
opon the threshold of his career. All the enormons periods 
that have gone before, with their straggles between ibis and 
that class of living creatures, culminate in the Poet-Pliooene 
period, with the predominance of a being who seems capable 
of controlling his own surroundings, and of forging ont new 
lines of progress for himself. In view of the long past, 
beside which human history is absolutely insignificant, the 
differences between individual men seem indeed of the most 
trivial character ; and we may look forward with confidence 
to the work which Man as a race may yet achieve. 

We now see how much William Smith and his fellow- 
workers have added to the interest and value of onr fossils. 
If we begin to examine any collection, we find that even 
fossils must first be studied in the open-air. We mnst 
not be content with the bringing together of chance speci- 
mens, preser\'ed as curiosities by a past generation, or picked 
out of the rubbish of a lumber-room ; we must collect intel- 
ligently for ourselves, sampling our district bed by bed, and 
comparing the general aspect of the fauna, when we return 
home in the evening, with the drawings and descriptions in 
the text-books. The determination of the exact species of a 
fossil is often a work of care and time, and we may have to visit 
our nearest scientific library, to refer to the figures prepared 
by the original author of the specific name. No one can be 
expected to carry the details of hundreds of fossils in his 
head ; and too much attention is often given to the learning 
off by heart of lists of species, when a few lessons in zoology, 
and m the general characters of successive faunas, would far 
better fit a student for appreciating Nature in the field. 

We are by this time not only armed with the means of 
assigning any particular fossiliferous series of strata to its 
correct epoch in the world's history, but we can also detect, 
through the evidence of fossils alone, the occurrence of any 
considerable unconformity. If we find, for example, Triassic 
fossils in a bed which rests upon one containing Devonian 
fossils, w(5 know that the intervening Carboniferous and 
Tennian beds were either swept away by denudation before 
the Trias was laid down, or were never deposited in this 
locality, owing to some upheaval that occurred at the close 



THE ANNALS OF THE EARTH 243 

of the Devonian period. We must always remember that we 
may find a fresh- water and a marine type of every system, 
while estiiarine beds elsewhere unite the features of the two, 
besides containing shells characteristic of brackish water. 

In due time the history of the most complex district can 
be unravelled, and we learn how many processes of construc- 
tion and destruction have been required to produce the 
surface-features that we see around us. " Stratigraphical 
geology " becomes, in fact, " Historical geology " ; and any 
notes that we may make on the beds in a local section, and 
on the fossils that we discover in them, may prove to be a 
serious contribution towards the completion of the annals of 
the earth. 



CHAPTER IX 

THE SURREY HILLS 

To apply the ideas gained in the last chapter to a special 
instance, we can scarcely do better than to visit the country 
to the south of London. There are few regions more simply 
beautiful, and few better known to the millions of dwellers 
in the south-eastern counties of England. 

Whether we reach the hills of Surrey by the London and 
Brighton Company's Portsmouth line, or by the South-Eastern 
Railway to Red Hill, the features traversed are much the 
samf;. We pass the brown gravel cuttings in the suburbs, 
the oozy clay-banks towards Croydon, and then emerge upon 
an open rolling country of dry chalky fields, leading up to 
clumps of little woods; the church-spires set among tiiem 
upon the rising ground show where the old villages have 
clustered. There is a steady incline from London south- 
wards, until we reach bolder hills with white chalk cuttings 
through them ; and at last the railway has to tunnel through 
a ridge, at Mickleham in the one case and at Merstham in 
the other. When we come out into the air again, we 
find ourselves leaving the face of a fine green range; a 
lowland, well wooded, with ponds and bric%ards scattered 
in it, stretches for a few miles before us; and then the 
ground rises again in the distance towards broken and fir- 
clad summits. 

If we reach Dorking, we can climb the highest point in 
the area, and make our suiTey from it, as we did from the 
Puy de l^ariou in Auvergne. Vive miles south of the town, 
Leith Hill rises, 967 feet above the sea ; and we make our 
way through the forest-land towards it, with a singular 
sense of freshness after the traverse of suburban London. 

From the summit we look over into several counties, in- 
cluding the whole of Surrey and its hills. Nearly all Sussex 
lies before us, and the borders of Kent are in the east. The 
features immediately around us are repeated, moreover, in 

244 



THE SURREY HILLS 245 

these three counties, wherever we come to the edge of the 
great chalky uplands. 

If we begin by looking north, we see a wide country, 
almost a plain, with a few flat-topped hills rising above it in 
the west, and one or two rounded summits far away in the 
north-east. On one of the latter, best seen at sunset, the 
Crystal Palace has been planted. Smoke and thick air hide 
the limits of this view ; but on a summer evening we may 
see the towers of Westminster, rising faintly in pink haze, 
and marking out the site of London. 

This is the area over which we rose slowly to the chalky 
plateau ; and we are really looking down the south slope of 
the valley of the. Thames. On the near edge of this region, 
the ground falls abruptly towards us, forming the long range 
of the North Downs, the surface of which is here ploughed 
over, here covered by thin yellowish grass, here broken by 
a great white quarry or a deep groove filled with trees. The 
brow of these hills is often marked by beech-woods, and we 
again see the church-spires along the edge, showing the 
position of high villages. Through one conspicuous gap, 
the River Mole wanders northward to the Thames, while 
Dorking is built upon a tributary which descends to join it 
from the west. 

At the foot of the sudden fall of the surface, there 
stretches a long band of low-lying meadows, through which 
this tributary takes its course. Then follows the rise to 
more broken country, and fir-woods climb towards us up to 
the very ridges of the hills on which we stand. This zone 
of the landscape is given over, indeed, to forest and to 
heather ; and Leith Hill itself is its culminating summit. 

The view southward is, however, far more striking. We 
are on the very edge of a second range of hills, nearly twice 
the height of those that lie north of us; on the west, in 
particular, the projecting masses of this range run out like 
promontories into the plain below. Far away, the curved 
front of these hills is continued by the long purple slope of 
Hindhead, the southern face of which also falls steeply into 
the lowland. The tops of all these promontories are formed 
by gently sloping plateaus, dipping towards the first range 
in the north ; the fir-woods cover these, and stretch in part 
over the steep southern side, shading ofiE there into thickets 
of beech and oak and underwood. 



246 OPEN-AIR STUDIES 

Below us is the pleasant conntiy of the Weald, the old 
forest-land that for long presented difficulties to the invading 
Normans. Now it is in great nieasnre cleared, and cut up 
into green pastures, with ploughed fields here and there. 
The roads and villages are marked by bands of elms, and 
large ponds gleam below us in the sunlight. Away in the 
east the great curved back of Ashdown Forest rises, dark 
with firs, out of this softer cultivated region. 

The Weald immediately in front of us knows no such 
interruption. The fields and hedge-rows stretch away for 
some sixteen miles, until they reach the foot of a row of 
hills which are somewhat hummocky and irregular. In 
August we may see on these, even at this distance, the 
purple of an almost continuous expanse of heather. But 
they are at times difficult to pick out against the slopes of a 
far bolder range that rises immediately behind them. Grey 
and distant, the South Downs there assert themselves as a 
long wave-like ridge on the horizon, with the beech-clump 
on Chanctonbury Ring standing out darkly and distincUy, 
800 feet above the sea. One or two deep notches show us 
glimpses of lower ground beyond, and on clear days the 
English Channel is visible in the gap at Shoreham. 

A telescope will soon reveal to us how the nearer and 
humbler range of hills sweeps round on the west to join the 
long mass of Hindhead. The South l>owns similarly dis- 
appear on that side into the rolling plateau of Salisbury 
Plain. The North Downs, which are continued beyond the 
gap at Guildford by the narrow ridge of the Hog's Back, 
also pass into this plateau, and are thus connected with 
their bolder southern rivals. Thus this end of the Weald 
is hemmed round with two approximately parallel ranges, 
the outer one bare on the whole, with short grass and a few 
beech-clumps, the inner one more broken, and dark with the 
broad masses of the fir-woods. 

The actual junction of the inner ridges, as they approach 
one another from north and south and unite at tiie western 
extremity of the Weald, is clearly seen in Harting Combe, 
six miles south-west of Haslemere. We descend by a rough 
sandy road from the high common into a narrow valley, which 
we cross close to its head. Here on three sides we are 
hemmed in by steep banks, covered with trees, while on the 
east side we look out into the broad Wealden hollow. In a 



THE SURREY HILLS 247 

few minutes we are climbing the opposite ridge, to an open 
heath similar to that upon the north. And then the view 
of the South Downs, rising picturesquely before us, with a 
line of villages in the lowland at their foot, repeats in all its 
essential features the view northward from Leith Hill. 

This regularity of features on both sides of the Weald 
must have some similarity of structure underlying it. If we 
study the ridges in detail, we soon see that the outer and the 
inner are composed of very different materials. Even from 
the summit of Leith Hill, we can perceive the series of white 
chalk quarries all along the face of the North Downs. They 
commence at a certain height up on the slope, which suggests 
that another material underlies this pure white limestone. 
Beyond Dorking, the Mole, excavating its channel against 
its eastern bank, has produced a fine natural exposure, the 
slope of Box Hill being there too steep for anything but a 
few clinging bushes. The white crumbling surface appears 
almost as a cliff, while woods of box and beech are massed 
above upon the plateau. 

But the forest-range, the dark jutting masses culminating 
in Leith Hill, show yellow sandstone in every section. The 
roads are paved with yellow blocks, the cuttings are yellow, 
and are often penetrated by the holes of sand-martins. 
What, then, is the relation of these two types of strata to 
one another ? 

Sections taken very near the surface may be misleading, 
since the higher parts of slopes always tend to creep down- 
wards, and there is in all such cases considerable shifting, 
even of the more solid deposits, by the action of gradual 
land-slides. But, if we take the evidence of a number of the 
deeper cuttings, such as we get in the beautiful lanes leading 
northwards through the fir-woods, we shall see that there is 
a steady slope of the beds of sandstone towards the hollow 
between the Leith Hill range and the North Downs. 

The angle which uptilted strata make with a horizontal 
plane is called their dip; more precisely, the dip may be 
defined as. the greatest angle that can be made with the hori- 
zontal plane by a line drawn in the surface of the stratum. 
If an exposed surface of the bed were perfectly smooth, 
water poured on it would run down in this direction of 
greatest steepness ; the line marked out by the water would 
also indicate the direction of true dip ; a vertical plane passing 



248 OPEN-AIR STUDIES 

through it would point either north, or south-east, or so forth. 
When we say that a bed dips is"" to the north-east, we mean 
that it slopes down most steeply towards the north-east, the 
angle made by its surface and a horizontal plane being 
15°. Or, to put it another way, if a vertical qnarry-faoe 
were carved out of this dipping series of strata, this face 
running N.E. and S.W., the strata would fall towards the 
N.E. end of the section, and their exposed edges would meet 
the horizontal floor of the quarry at an angle of 1 5^ 

In determining the amount of disturbance of strata, and 
their relations to one another, we require some instrument to 
accurately indicate the dip. If our quarry-section or natural 
cliff does not lie in the direction of true dip, the angle 
observed will be smaller than that required ; and the largest 
of a number of afparent dips thus collected will be nearest 
to the true angle. It is easy, however, to make a geomet- 
rical construction to determine the true from any two ap- 
parent dips.i Where a large smooth surface of a stratum 
is exposed, the direction in which a cutting must lie to expose 
the true dip can be found as follows : — Take a spirit-level with 
a fairly long base, and move it about on the surface until the 
bubble becomes central. Place a walking-stick, resting on 
the same surface, perpendicular to the straight edge of the 
spirit-level. The stick lies in the direction of greatest steep- 
ness ; it shows to what point of the compass the bed dips, 
and the complement of the angle between it and another 
stick held vertically at its lower end would give us the 
amount of the true dip. 

To measure the dip in any section, a clinometer, or " in- 
clination-measurer," is required. This can be very simply 
made. Draw a semicircle on cardboard, with a radius of 
about 6 centimetres, and divide it, like a protractor, into 
180 degrees. Place the base upwards and number the 
lowest point of the curve 0°, and continue the numbering 
up to 90° on either side, the two points marked 90° being 
thus on the base-line of the semicircle. Glue the card down 
on to a flat well-squared piece of wood about 20 cm. by 8 
cm. ; the top of a cigar-box provides good material. The 
base of the semicircle must be near to and accurately parallel 
with one of the long edges of the wood. Then press a draw- 

* See " Aids in Practical Geology," p. 6 ; and W. H. Dalton, Geol. Mag., 
i»73. p. 333- 



THE SURREY HILLS 



249 



ing-pin nearly home into the wood through the centre from 
which the semicircle has been described. Hang a dark thread, 
by a loop at one end, from the drawing-pin, and attach a 
small weight to the other end, so that it hangs freely below 
the semicircle when the long edge of the instrument is held 
horizontally. The clinometer is now complete. 

To determine a dip, stand some seven or eight yards from 
the face of the section, and hold the clinometer in a plane 
parallel to it. Then adjust the long top edge until it appears 
to coincide with the exposed edge of one of the strata. The 
pendulum, formed by the weight and thread, of course still 
hangs vertically, and the reading where the thread crosses 
the arc shows how many degrees the edge of the stratum 



North Downs 







Le/th Hill 
range 

3 Weald 




Fig. 21. —Section across the Surrey Hills. Vertical scale neablt 

three times the horizontal. 

I, Wealden Beds ; 2, Atherlield Clay ; 3, Hythe and Bargate Beds ; 4, Folke- 
stone Beds ; 5, Gault Clay ; 6, Upper Greensand ; 7, Lower, Middle, and 
Upper Chalk. 



deviates from the horizontal. The direction of the face of 
the section is obtained with an ordinary compass. 

The dips of our Leith Hill sandstones are found to be 
but small, 5° being common; but that is quite sufficient to 
bring them, if continued northward, well under the ridge of 
the chalk Downs. Indeed, in the distance of four miles, 
and with their relative heights, a dip of 2° would do so. If 
we examine in turn the quarries of the soft white limestone 
known as chalk, which we find forms the mass of the North 
Downs, we see that this series of strata also dips northward 
at a similarly low angle. Away in the Hog's Back, between 
Farnham and Guildford, the dip rises to 40° ; but this is 
quite exceptional for the Surrey Hills. 

Following out these observations all round the Weald, we 




2 50 OPEN-AIR STUDIES 

find the dips becoming N.W. near Famham, then W., and 
finally S., as at Harting, and Arundel, and Brighton. The 
beds have been bent, then, into a flattened ellipsoidal dome, 
something like the roof of a great elongated public hall. 
One end of the dome lies in Salisbury Plain, and east of this 
the top has been worn away, the two most resisting layers 
of which it was composed standing up to form the ridges 
round about the Wealden area. Such ridges are called 
escarpments. For their production we must have strata 
more or less inclined (fig. 21); the weathering eats its way 
along one of the sloping surfaces between two beds or series 
of beds, and cuts back the upturned faces of the beds lying 
above this plane. The ground at the foot of an escarpment 
is thus formed by the dipping surface of the underlying 
series of strata ; the face of the escarpment is formed by the 
joint -surfaces of the overlying series, which allow the rock 
to weather down steeply, the slope being of course only in 
rare cases a vertical cliff, and being usually banked over 
with long taluses. The back of the escarpment is formed by 
the dipping surface of the beds which have given rise to it, 
and from which some other series of strata has probably been 
removed. 

The ridges formed by the upturned edges of the beds that 
we crossed on the sea-shore (p. 92) are excellent models of 
escarpments. The dipping surface between the edge of one 
escarpment and the foot of the next is called the dip-slope, 
and is usually, in examples on a large scale, inclined to the 
horizon at a slightly less angle than the strata themselves. 

While escarpments may be worn out, even where the 
successive upturned strata are of equal hardness, by the 
giving way of the rock, block by block, along its planes of 
bedding and of jointing, yet on a large scale in nature their 
formation is greatly facilitated by the occurrence of a hard 
or a tough resisting bed above one more liable to be worn 
away. The general tendency of denudation is to wash down 
the surface evenly ; but the exposed edge of the soft bed is 
cut down more rapidly, the more resisting one standing out 
above it as an escarpment. Kivers will flow in such cases in 
the hollows thus worked out, approximately at right angles 
to the direction of dip of the strata, and will continually 
undercut and perpetuate the escarpment. Their tributaries 
ill flow down on one hand from the underlying dip-slope. 



THE SURREY HILLS 2$ I 

and on the other from the steep face of the escarpment. 
The dip-slopes will thus be channeled by subordinate valleys, 
the streams in which run parallel to the direction of the dip; 
while the escarpments will be cut back into combes by streams 
parallel to the foregoing, but running in the opposite direc- 
tion, i.e,, away from the point towards which the beds are 
dipping. Between the action of the main stream in the hollow 
and the tributaries in the combes, the face of the escarpment 
is continually receding in the direction of the dip, while it 
comes to have a wavy form, owing to the picturesque hollows 
locally carved out in it by the tributaries. 

There is one direction, and one only, in which a horizontal 
line can be drawn in the surface of an uptilted stratum. 
That direction is called the strike, from the German word 
Streclce, meaning the " stretch " or " extension " of the bed. 
This line is perpendicular to the direction of the dip ; and it 
is clear that the general trend of an escarpment will be in 
the direction of the strike. 

If the strike of a bed varies, the direction of dip must 
vary also, its amount remaining or not remaining the same. 
If the direction of dip remains the same, but its amount 
varies, the strike remains unaltered ; but it must be noted 
that beds dipping in exactly opposite directions have the 
same strike. A horizontal bed may be regarded as striking 
in all directions, or as having no especial strike. 

We have seen how the northern escarpments in the 
Surrey Hills are repeated away in Sussex on the south. 
The long blue bands that lie there facing us are the opposite 
limbs of a great fold, which is five-and-twenty miles across. 
Every escarpment must thus, at some time or other, have had 
its continuation in some opposite slope. Possibly the strata 
may have been bent over into a horizontal position, and may 
have so extended for some distance; but eventually they 
must have sunk on the other side approximately to the level 
that they occupied in the crust before the formation of the 
fold. An upward fold of this kind, the ridge of which may 
be sharp or broad, is called an anticlinal, from the fact that 
the beds dip in opposite directions on either side of the 
ridge ; while the corresponding fold, in which a trough is 
produced, is a synclinal, the beds sloping towards one 
another and forming the floor of a depression as they meet 
(fig. 32). In folded strata, as we shall see in the next chapter. 




252 OPEN-AIR STUDIES 

anticlinals and synclinals may follow one another in quick 
succession. 

Thus the dip of beds may vary in amount, and may 
reverse itself in direction, again and again in a short stretch 
of country ; and then the general lie of the strata is best 
described by saying that they are repeatedly folded, but that 
they strike in such and such a direction. 

If we keep in mind what we have before our eyes in the 
west end of the Weald, we shall never forget that an anti- 
clinal mass is not quite so simple as it appears when we draw 
a diagrammatic section across it. It must have a termina- 
tion somewhere on this spheroidal earth; there must be a 
point where the beds will dip down outwards in a constantly 
dianging direction, untU we get round to tlie other mai^ 
flank of the anticlinal. That is the feature presented to ns 
at Harting Combe. If we have strata pushed up as a mere 
dome, like that of a cathedral, any one bed will dip outwards 
in all directions from the apex of the dome formed by it. 
An anticlinal mass is merely such a dome greatly extended 
in one direction ; and this dome-like character will be obvious 
at the two ends of the fold, which may be a few yards or 
many miles apart 

If the action of denuding agents has planed a smooth 
horizontal surface across a set of tilted strata, the area occu- 
pied by each bed on the surface will depend upon the angle 
of dip (fig. 22). If the dip is vertical, or 90°, the width of 
the band formed by a bed on the surface is equal to the 
thickness of the bed ; but it widens out as the bed dips at a 
lower and lower angle. The extreme case is where the bed 
becomes horizontal, when it covers the whole level surface, 
concealing the other strata beneath it. Hence, the more 
nearly horizontal a bed is, the more we see of it in traversing 
a level country, and a thin layer of rock may then often seem 
to have a great importance. 

The area of a bed exposed at the surface of the earth is 
called its outcrop ; and the extent of this will be similarly 
affected if the beds are horizontal and if the surface formed 
by denudation cuts across them (fig. 22). On the face of a 
cliflf formed in horizontal strata, the true thickness of each 
bed is seen; on the gently sloping sides of a valley, the 
tcrops become far more extensive. 

Thus the outcrop of a bed depends on its dip and on the 



THE SDRREY HIU8 



253 



angle and direction of the denuded surface ; a bed may, for 
instance, by reason of its dip, eraei^e perpendicnlarly to the 
face of an escarpment, in which case the width of the ont- 
crop is of course again eqnal to the thicbnesB of the bed. 

Here we have the secret of the difference between the 
narrow ridge of the Hog's Back near Guildford and the 
typical brood plateau of the Downs. The steep dip in the 
former region (p. 249) enables all the thickness of Chalk to 
appear in the limits of a narrow outcrop, the dip-slope 
being at least as steep as the face of the escarpment ; while 








Th9 beds lae nil of tho snme thicknees, but the outcrop of B is fur wider thnn 
thnt of A or c, although the throe beds are horizontal. The outcrop of the 
bed nt b ia wider on ft horiiontnl surface thnn at D, owiDg to ft lesseiiing of 



the very low average dips in the ordinary North Downs 
spread out the onbcrop over a width of many miles. 

Another striking feature of onr Surrey landscape demands 
an explanation before we study the beds in detail. The River 
Mole seems to defy the physical structure of the country. It 
rises in the fairly low ground of the northern Weald, where 
its higher tributaries wander down from the slopes of St, 
Leonard's Forest, and bring with them a good burden of 
clay and sand. But at Dorking it meets and cats through 
the Chalk escarpment, making a valley 300 feet deep, and 
then flows rationally down the dip-slope towards the Thames 
at Ditton. All the great streams of the district follow this 



254 OPEN-AIR STUDIES 

strange example, and both the North and South Downs are 
cleft by Bteep-sided valleys. Instead of draining eastward, 
nnder and along the faces of the escarpments, the Weald 
sends its waters north and south directly across the ridges of 
the hills. We can thus see the gap of the Wey near at hand 
at Guildford, and before us the notches of the Aron and the 
Adour, deeply indenting the dark sand-ranges and the South 
Downs. The water cannot have run up the faces of these 
escarpments and then have carved its way down to its former 
level ; the only probable conclusion, from a careful inspec- 
tion of the country, is that the rivers are older than the 
escarpments. 

They began to flow, in fact, when the great anticlinal 
of chalk was first lifted above the sea, and when its ridge 
was first attacked by denuding agents. Tlie main drainage- 
lines would thus naturally lie down the dip-slopes to north 
and south. Gradually the tributaries of these main streams, 
working between the harder and softer strata, b^an to 
cut out the east-and-west escarpments; but the valleys 
which were already excavated down the dip -slopes pre- 
vented thesf? new ridges from being continuous, and the 
yielding materials that fell a prey to the lateral streams 
were still swept out of the district by the north-and-south 
main routes. 

Some of these gaps are, however, more recent than the 
escarpments, and result from the cutting back of the head- 
waters of a stream, until the col between it and the Wealden 
hollow has become obliterated. At Merstham, between 
Croydon and Red Hill, the north-and-south valley of 
Smitham I^ottom, no longer occupied by a stream, runs 
gently up to a little pass, whence the ground falls more 
steeply on Red Hill. Had the former conditions of rainfall 
continued, this deep notch in the North Downs would have 
been worked back, would have been deepened another 200 
feot or so, and communication would have been opened 
here between the streams that descend from the sand-range 
and the Thames. The chalk escarpment, at any rate, would 
have received an additional breach. Immediately to the 
east, above Godst^ono, the old northward-running river of 
the Caterham valley worked its way back perilously near 
to the face of the escarpment^ and already, at the time of 
its extinction, had cut a valley 250 feet deep across the 



THE SURREY HILLS 2 55 

ridge. Such a river, if it once succeeded in entering the 
Weald by the backward movement of its head, might inter- 
sect the course of some eastward-flowing stream, which 
was engaged in cutting the escarpment, and might entirely 
draw off its lower waters into a course right through the 
ridge. (Compare p. 85.) 

Thus, by deep scorings of the dip-slopes, and by a 
general scouring out of the beds in the heart of the great 
anticlinal, the beautiful variety of landscape that spreads 
before us has been produced. The very core of the Weald 
is formed by St. Leonard's and Ashdown Forests, where 
sandy strata, the lowest of the folded series, are exposed. 
The anticlinal movement has brought them, at Crowborough 
Beacon, 800 feet above the sea ; but at our west end they 
are sunk below a series of clays which form far less bold 
a feature. It is time now to descend the face of Leith Hill, 
and to leave the wild heath and forest for these cultivated 
lands. In the roadside-cuttings and the Wealden brick- 
yards we can begin to study the course of events before 
Surrey and its hills were dreamt of. 

The general assemblage of fossils, which have been 
diligently collected in this district throughout the nineteenth 
century, shows that the Weald and the surrounding ridges 
are alike formed of Cretaceous strata (p. 231). In the 
Wealden series we have the base of the system, since the 
very top of the Jurassic beds peeps out directly under them 
in the neighbourhood of Hastings. 

The lower beds of the Wealden dome are mainly sand- 
stones, forming loose sandy heaths near Tunbridge Wells, 
across which it is impossible to make permanent cart-roads. 
In a few gitty bands and clays associated with them, fresh- 
water fossils have been found. The spirally coiled univalve 
mollusc Paludina is perhaps the most noticeable; it still 
lives abundantly in rivers and in inland seas in all quarters 
of the globe, and whole beds of limestone, such as the 
" Sussex Marble," are made up, in the Wealden series, of 
its remains. The little spiral shells are well seen in section 
when the rock is sawn and polished; and the famous 
" Purbeck Marble," used so largely for the shafts of small 
columns in our cathedrals, is a similar stone from the upper- 
most Jurassic strata. 

A few bivalves occur, of genera that typically inhabit 



256 OPEN-AIR STUDIES 

fresh or brackish water; their presence snpportB the view 
that these beds were formed in the broad waters of a lake.^ 
A nnmber of fish-remains have also been foDnd; bnt the 
most remarkable back-boned animals of this epoch were 
nndonbtedly the gigantic reptiles. 

In 1822 Dr. Gideon Mantell discovered certain teeth 
in the sands near Cnckfield in Snssex; and he named the 
animal to which they belonged Ifpianodon, since, in their 
flattened form and saw-like edges, they resembled the teeth 
of the living Sonth American reptile Iguana. It often 
happens that a name mnst thus be given to fossil remains 
before any considerable portion of the animal is discovered. 
In 1834 a number of large reptilian bones were found at 
Maidstone, together with the c»st of a tooth and the frag- 
ment of another- similar to those already known; and, 
later, detached bones were found all through the Wealden 
deposits. The animal was now known to be a formidable 
creature, although vegetarian in its habit& More recent 
discoveries of the same genus in Belgium have shown that 
it was from eighteen to thirty feet in length ; its hind legs 
were longer and altogether more powerful than its fore 
legs, and it walked fairly upright upon them, dragging its 
huge tail behind it on the ground. 

There were other genera of reptiles also in Wealden times, 
including crocodiles; and among the largest was Megalosaurus, 
which was a flesh-eater, judging from its teeth. This creature 
was about twenty-five feet long ; but Cetiosaurus, a vegetable- 
eater, surpassed it, some species being nearly forty feet long. 
The Wealden Cetiosaurus is only known, however, by a few 
bones, mostly separately scattered in the deposits.' 

The trees surrounding the lakes and rivers were far dif- 
ferent from those prevailing now-a-days in the Weald. Not a 
beech, nor an elm, nor an oak existed, as far as we know, upon 
the surface of the earth. There were forests of conifers, like 
those now massed darkly on Leith Hill, and tree-ferns grew, 

» See A, Jakes-Browne, " The Building of the British Isles," p. 268. 

* Mantell, "Medals of Creation," 2nd edit., vol. ii, p. 691 ; «« Wonders 
of Geology," 6th edit., vol. i, p. 422 ; Hutchinson, '* Extinct Monsters," 
pp. 82-89. 

' For the variety of these reptilian remains, see R Lydekker, " On a New 
Wealden Iguanodont and other Dinosaurs,** Quart. Joum. OtoL Soc, voL xliv, 
p. 46 ; and for a general account, with restorationss see H. N. Hutchinson, 
" Extinct Monsters,** pp. 59-108. 



THE SURREY HILLS 257 

picturesquely spreading, on the river-banks. A group of 
comparatively short and thick-stemmed trees, the Cycads, 
unknown to us now in a wild state in Europe, abounded then 
throughout England. They are allied to the conifers, and are 
thus regarded as low and humble among the flowering trees ; 
and at present they have to be imported from the tropics. 
All these plants are represented by stems and leaves washed 
into the beds of Wealden clay and sandstone ; and the fre- 
quency of patches of lignite is another piece of evidence in 
favour of the fresh-water origin of the Wealden strata. 

The higher beds, which spread before us from the foot of 
Leith Hill, and which, indeed, form much of the bulk of the 
range itself (fig. 21), are composed of a fairly pure clay, 
sometimes looo feet in thickness. The surface is often 
damp, and oak-thickets abound upon it ; the roads running 
through these woods are sloughs of despond after heavy rains, 
and the pathways in more frequented districts are raised upon 
causeways to keep them above the level of the floods. The 
brick-yards show us brown and blue sections in the clays, 
often variegated by red and almost crimson stainings. These 
colourations, due to hydrated iron oxide, are also a character 
of lake-deposits (p. 142). On the surfaces of some of the 
more shaly beds we may find white relics of univalves and 
bivalves, like those in the clays among the lower sandstones ; 
and tiny ostracod shells, looking like little split seeds, cover 
large areas characteristically. The ostracods are simple crus- 
taceans which live in bivalve shells of their own making; 
and the detailed examination of the Wealden genera shows 
that many agree with those living in fresh water at the 
present day. Others, however, are extinct, and are thus use- 
less for indicating the character of the Wealden waters. 

All through the Wealden series,beds of sandstone cemented 
by rich brown limonite, or nodules of iron carbonate and 
oxide in the clays, have been dug out in former times for 
iron-smelting. As long as coal and iron ores were but little 
worked in the north of England, and as long as wood was 
freely available for fuel, this work went profitably forward ; 
and now and again we may turn up the old slags from the 
furnaces, like fragments of volcanic glass, in some forsaken 
comer of the woodlands. From the thirteenth century to 
1828 ^ the Wealden iron was extracted ; and the discovery of 

* H. B. Woodward, " Geology of England and Wales," 2nd edit., p. 361. 

R 




258 OPEN-AIR STUDIES 

coal in deep borings at Dover may some day again convert 
this garden of England into a fuming industrial centre. 

Once more we have in these iron-ores an indication of 
lake-deposition, limonite being produced freely in such waters 
(p. 142), and soluble salts of iron being always present among 
the materials brought down from wooded shores. 

Away in Dorsetshire, east of Lulworth, red and yellow 
clay-beds occur between the Jurassic limestones and the 
Chalk ; and these mark the westward prolongation of the 
ancient Wealden lake. Its east end lay beyond the present 
Channel near Boulogne. So we may picture some 170 miles 
by 50 covered in early Cretaceous times by an inland sea, 
the floor of which sank as successive sand-banks and mud- 
banks were spread out in it. Plants of humbler groups, 
partly tropical in character, formed a kind of jungle on its 
banks, dense enough to provide food for the massive Iguano- 
dons, which stalked about heavily and unhindered, their heads 
fifteen feet in air. Every now and then a crocodile snapped at 
the fishes among the leafy islets, half hidden by the natural 
rafts of fallen stems ; while a Megalosaurus, looking out for 
some of the smaller quadrupeds, crashed through the jungle 
and left its footprints in the yielding swamp. Beetles 
hummed and crawled among the bushes; but none of our 
flowers, and none of our honey-sucking insects, enlivened the 
borders of the lake. 

Slowly the sea began to creep in over the land, and the 
great lake became a tidal estuary ; marine shells, including 
oysters, took up their abode in it ; and the final muds of the 
Wealden stage contain a distinctly salt-water fauna. The bed 
above, the Atherfield Clay, is the first of a new series, which 
ushers in a long epoch of steady depression of the land. 

So far we have pictured the reptiles as lords of the 
Wealden world. Birds must have existed, but their bones 
have not yet been forthcoming; such light remains would 
easily become scattered and broken up, and probably only a 
few individuals actually dwelt in the more secluded comers of 
the forest. The earliest known bird comes from the higher 
Jurassic strata of Germany, and is represented by two winged 
skeletons and an isolated feather. But for the feathers on the 
wings and tail, the creature might have been regarded as a 
reptile. For at this time the reptiles had also taken to the 
air ; the whole empire of the globe seemed open to them, and 



THE SURREY HILLS 259 

they grew huge and ponderous, having little need of excep- 
tional intelligence to keep their predominance secure. No 
rivals seemed to threaten them. Some marched across the 
land, browsing on the tops of the cycads and tree-ferns ; 
others, with long necks and cruel teeth, pounced down upon 
smaller creatures, crushing them with one stroke of their 
massive feet ; others took to the sea, just as the mammalian 
whales did in later times, and became beautifully modified to 
suit their new surroundings, grasping, either by length of 
jaw or the sweep of a swan-like neck, the fishes that had 
long been secure from the attacks of higher beings. And 
other reptiles, again, provided with membranous wings, which 
were stretched from the enormously long outer finger of each 
fore-limb to their sides, flew through the air, and clung with 
claw-tips and wing-tips, like bats, to the faces of the crags. 
The earliest birds, as we have said, closely resemble feathered 
reptiles, and it is scarcely surprising that they also should 
have been armed with teeth. Probably they prevailed 
against the flying reptiles mainly by their power of more 
rapid and prolonged flight, and often, having hidden them- 
selves from a pursuer in some dense-leaved tree, were dis- 
turbed again by the head of a prowling reptile looking down 
on them as he strolled across the forest. The voices of a 
flock of toothed birds, rising clamorously from the mud-flats 
of the Wealden lake, can hardly have been pleasing to the 
ear. Their long jaws would gape, showing the sharp teeth, 
like those of crocodiles ; their feathered wings and tail would 
seem quaintly contrasted with their downy or almost naked 
bodies ; and only their more elegant movements in the air 
would show what a step forward had been made in the great 
line of animal life. As we cross the pastures and copses of 
the Weald in spring, when every bank is starred with prim- 
roses, and every bush seems to leap with sparrows, and 
linnets, and cheerful chaffinches, it is hard to think of the 
same region in early Cretaceous times, when birds were few 
and of strange and forbidding types, and when all this carpet 
of delicate flowers was as yet unknown in the wide world. 

In the United States, Cretaceous birds are known, later in 
date than the deposits of the Weald ; it remains for some 
happy observer to turn up a bone or two in south-east Eng- 
land as a link between these and the specimens from the 
Jurassic beds of Germany. 



26o OPEN-AIR STUDIES 

We are equally ignorant regarding the highest animals, 
the mammals, of the period The higher Jurassic beds of 
Britain have yielded jaws and teeth ; the uppermost Creta- 
ceous rocks in America have shown similar remains ; and all 
we know is that the mammals of the Weald must have been 
of lowly character, humbled and kept under by the over- 
whelming power of the reptiles, and seeking their food by 
stealth almost between the legs of these great beasts. They 
must have been about the size of rabbits and foxes, with a 
considerable variety of teeth and modes of feeding ; and we 
can picture them scuttling into their holes and lairs among 
the underwood, whenever the neck and chest of a great 
lizard began to sway the fronds of the tree-ferns. A certain 
quickness of apprehension, and ingenuity in the face of 
danger, must have been bom in them during these long 
years of repression ; and in later times, when the reptilian 
empire became doomed, the mammals naturally stepped into 
the gap, speedily ran riot across the jungles and the plains, 
and even entered the expanses of the sea. In Wealden 
times, however, they were of the humblest character, belong- 
ing to divisions at least as low as the monotremes and the 
marsupials, which zoologists place at the very bottom of the 
long series of existing mammala 

With the deposition of the Atherfield Clay, the Wealden 
area was invaded by the sea ; and this stage is named from 
a spot on the south side of the Isle of Wight, where the 
beds are admirably fossiliferous. In the Wealden area, 
they form a portion of what we have called the sand-range, 
since they are protected by the more resisting beds above, 
and the front of the escarpment is cut down across them ; 
but they naturally produce a more gentle slope than that 
given by the yellow sandstone. Above this stiff blue clay 
come the "Hjihe Beds, named after a Kentish watering- 
place. These are fairly firm sandstones, with grey shelly 
limestones among them as we go eastwards into Kent. In 
the Leith Hill area they seldom contain fossils, and we have 
to trace them over long distances before we can find a 
satisfactory fauna. A few plants were still being washed 
in from the land, and there are thus at intervals soft black- 
brown beds of lignite. The rock is quarried into for road- 
metal, and is seen in all the shallow pits which form patches 
of yellow through the dark woodland of Leith Hill. The 



THE SURREY HILLS 261 

roads that crosB the ridge are also bonnded by little sand- 
stone clifEB, in which the stratification can be seen. East 
and west, the bold escarpment of the Hythe Beds stretches, 
the finest feature of Bouth-eastem England; and, as we 
ahall presently see, it owes its or^n mainly to the humbler 
organisms that lived in the Cretaceons sea. 

The superior resistance of the Hythe Beds to denudation 
is, in fact, largely doe to the numerons beds of flint ^ that 
are contained in them. In these beds the sand-grains are 




cemented by chalcedony, forming a brownish translucent 
rock of smooth fracture ; the flint-layers thus constracted 
run along the stratiflcation-planes, with more friable and 
pale yellow sands between them. Here we can pick up a 
fragment with three or four flint bands in a thickness of 
two inches; and in some of the little qaarries we can choose 

' TheSH are coniinoDly called "chert," but it ia impnettible to make any 
distitictiun between tliia material aad flint Tbe U[)per Jursasic nudnlar 
"cherts" uf Doraetsbire, fur inatancti, are precisely like tbe "fliata" of tbe 
Upper Chalk, 



■\ 



262 OPEN-AIR STUDIES 

large specimens which look like a pnre pink-brown chalcedony 
throughout. 

Down near Friday Street, for instance, some of the 
rough tracks through the forest are paved with translucent 
flint, just as some of the roads north of the Auvergne pnys 
are paved with agates from the mines. If we look at these 
with a lens, we see an immense number of delicate white 
rods in them, reminding us of crystals in a glassy rock. 
These are the dull casts of sponge-spicules, which themselves 
originated the flint. 

Our common modem sponges, such as we use in washing, 
have homy fibrous skeletons ; but others, like the beautiful 
"Venus's flower-basket," make their meshy skeleton of 
silica; others, again, strengthen themselves with rods and 
three-rayed stars of calcium carbonate. Sponge-skeletons 
are built up of minute rod-like or often knotty bodies 
known as spicules, which frequently fall apart atfter the 
death of the animal and are scattered over the sea-floor. 
In many cases, moreover, this distribution is made easier by 
the fact that the spicules are only loosely interlocked to form 
the skeleton, or are merely embedded separately in the sub- 
stance of the sponge. Sponge-oozes are made up at the 
present day of such remains. The siliceous spicules (fig. 23) 
are composed of amorphous silica, and not of quartz, and in 
this condition are liable to subsequent attack by the solvent 
action of the sea. The rod-like forms are traversed by tiny 
canals, so that they resemble, when broken, pieces of fairy 
thermometer-tubes; and the water slowly rounds the ends 
of the fragments and enlarges the central canal, finally dis- 
solving the spicule altogether. Thus sponge-beds, like parts 
of coral-reefs and shell-banks, are removed in solution ; but 
the material, wandering in the water near the ocean-floor, 
may be again chemically deposited and may consolidate as 
beds of flint. 

The complete solution and re-deposition, however, pro- 
bably do not occur until the sponge-bed is covered over by 
other sediments and becomes subject to the slow attack of 
the waters that permeate the earth's crust.^ These waters, 

^ The rare cases in which silicificatioD has gone on in modem oozes seem 
attended with the production of silicates rather than of opaline or chaloe- 
donlc silica. See "Report on Deep Sea Deposits," Challenger ReporU, p. 390^ 
and pi. xi. 



THE SURREY HILLS 263 

moving along the bedding-planes of the strata, spread out 
the silica into more or less regular bands. 

Sponges are by no means the only organisms that extract 
silica from sea- water ; and we must expect to find remains 
of radiolarians, and of the tiny skeletons of the plants called 
diatoms, associated with beds of flint. As a matter of fact, 
however, solution has generally been pretty effective, arid we 
have only the dull earthy moulds of sponge-spicules left 
to us, these spicules being bodies of comparatively coarse 
dimensions. The original substance of the spicules, and 
probably also of associated diatoms and radiolarians, is seen 
in the chalcedony round about the spicular casts. 

These little rod-like relics are well worth looking for in 
the " cherty " layers ; the silica has also enclosed the sand- 
grains and any other solid bodies that were in the stratum. 
We shall presently see, on the bare front of the North Downs, 
how silica is deposited with somewhat different results in the 
heart of massive limestones. 

All the sandy layers of the Hythe Beds are " Green- 
sands *' (p. 107) ; and the prevalence of grains of glauconite 
(fig. 23) in these and in the overlying strata has caused the 
whole of the stages from the Atherfield Clay to the top of the 
Folkestone Beds to be called the " Lower Greensand," a name 
by which they are often known on maps. The glauconite 
grains give a dark speckly character to the rock, and come 
out as brilliantly green oval spots in microscopic sections. 
When walking through the Surrey lanes on a damp day, we 
may strike our hammer into the sandy wall of some roadside 
cutting ; and the soft glauconite becomes crushed and spread 
out, so that the mark left by the hammer appears distinctly 
green. 

Glauconite indicates, if we may judge from existing seas, 
that these sandstones were deposited in water fairly near the 
land. The beds are sometimes composed of coarse sand- 
grains, and we shall find real pebbles nearer Guildford ; while 
the current-bedding also points to a shallow-water origin. 
The most interesting deposits are those at the top of the Hythe 
Beds, where a rough limestone, the Bargate Stone,^ occurs. 
Besides marine shells, including f oraminif era, such as lived on 
the Cretaceous beaches, we find this rock full of rolled fossils 

^ For recent work on these beds see F. Chapman, " The Bargate Beds of 
Surrey," Qtmrt, Jouim. Qed, Soc., vol. 1, p. 677. 



264 OPEN-AIR STUDIES 

derived from Jurassic beds. The dark little grains which are 
so frequent in the Bargate Stone prove to be wave-worn 
fragments of casts of moUuscan shells, belonging to the 
preceding period. Oolitic grains, brought in from Jurassic 
limestones, spines of sea-urchins, and pieces of older flints, 
are found mixed together in this deposit. We have, indeed, 
to be careful in distinguishing the rolled and derived fossils 
from the remains of the animals that were living when the 
limestone was accumulated. 

Such a discovery gives us at once a picture of the coast on 
which the Hythe and Bargate beds were formed. No Juras- 
sic rocks now appear in this area ; but they have been found 
at a depth of 11 50 feet below the surface in a boring made 
at Eichmond in the north of Surrey. They come out, again, 
from under the Cretaceous "greensands" at Oxford and 
Swindon on the north-west, and under the Wealden clays in 
the Isle of Purbeck. From a boring near Hastings it is 
known that a great thickness of them underlies the Weald. 

Now, under Eichmond the Cretaceous rocks are succeeded 
directly, as we go downwards, by the Middle Jurassic series ; 
the whole Upper series is missing — we are in fact in pre- 
sence of an unconformity. The material washed away from 
the top of the Jurassic system during its period of exposure 
went to make up the Bargate Beds, and indeed a great part 
of our Lower Cretaceous seriea 

The coast of Dorset, in fact, at the present day, repeats for 
us the shore of the Lower Cretaceous sea near London. Be- 
tween Portland and St. Alban's Head we have many stretches 
of bay, in which pebbles and fossils from the Upper Jurassic 
sands and clays and limestones are being mingled with the 
shells of the period in which we live. We may picture such 
a coast lying to northward of the Weald, and slowly being 
encroached on by the sea. At one time the rounded lime- 
stone hills, with little river-gorges cut in them, sent down 
their waters into the Wealden lake ; but in the days repre- 
sented by the Hythe Beds the sea had encroached, and was 
already lapping round their feet. Cliffs were cut out, huge 
blocks of Jurassic limestone were broken up by the waves, 
and their fossil contents were scattered on the beach ; and in 
most cases only fragments of the more resisting materials 
remained recognisable amid the rolling mass of pebbles. 
Down souths where Leith Hill was afterwards to rise, many 



THE SURREY HILLS 265 

of these fragments, together with derived oolitic grains, be- 
came washed out into quieter waters ; and here Cretaceous 
shell-banks stopped them and caused them to accumulate. 
It is pleasing thus to see how many details of the past can be 
brought before us by the study of a single cutting in the Bar- 
gate Beds, and by a careful sorting out of their constituents. 

So the floor on which the marine Cretaceous strata here 
rested was unconformable to them, as must always be the 
case when we near a shore-line ; and so far Jurassic strata 
were being used up again to make the Leith Hill sand-banks. 
Gradually the bays in this coast must have become filled 
with the broad stretches of the sand; for the Folkestone 
Beds, the next in upward order, are typically loose current- 
bedded materials, with all the character of sand-flats off a 
coast. Fossils are very scarce, owing to the porous nature 
of the beds, which has allowed the shells to be dissolved away 
by rain-water ; and limonite cements the sand-grains along 
irregular water-ways, forming bands of dark brown "iron- 
stone," which stand out sharply upon weathering. Here 
strongly orange, here almost white, here a delicate warm 
brown or even pink, these sands form a beautiful feature of 
the lanes on the north fringe of the fir-woods. Then we 
emerge upon quite another country, the long hollow of the 
pools and streams. 

Here is a fortunate little quarry, north of the Dorking 
and Guildford road, which shows us the actual junction of the 
Folkestone Beds with those above. The variegated sands, 
perforated by the nests of martins, pass somewhat abruptly 
into beds of stiff blue clay. Perhaps the denuding agents, 
working on the Jurassic rocks, began to wash down clays in 
place of sands; perhaps the sea-floor sank rapidly, and the 
finer materials alone could be deposited in this area. Cer- 
tainly this clay, known as the Oault, is distinctly marine in 
character. When examined minutely, a good deal of sand 
and glauconite can be discovered in its lower portion ; and it 
is well worth while to collect a specimen for the sake of the 
microscopic objects that it contains. If we dry fragments of 
the clay thoroughly on a dish in an oven, or on a metal plate 
over a Bunsen-bumer, and then place them in a soup-plate 
full of water, they will break up with remarkable readiness 
into a very fine-grained mud. The finger must not be used 
to assist the disintegration of the lumps, as the particles 




266 OPEN-AIR STUDIES 

would thus become pressed together into clots ; but a circular 
swaying motion must be given to the plate, by which the 
water becomes quickly thick and muddy. The water is then 
poured off gently, and more is added, the process being 
repeated until the lumps are entirely broken down and the 
greater part of their substance has been washed away. The 
residue contains any sand, glauconite, and shells that were 
concealed in the mass of the original clay. As usual, sifting 
will assist in dividing up these materials; the larger-sheU 
fragments will remain in the 30-hole sieve (p. 105), and in 
6ohole or 90-hole we shall find a number of exquisitely pre- 
served foraminifera. Where these, however, are required 
in their most perfect condition, we must be content with 
thoroughly washing oft the clay from them by swirling them 
about in a little water in the soup-plate, and then must select 
them by picking them out separately with a moistened and 
pointed piece of wood or a fine brush. In this way even 
the delicate knobs and spiny projections on the ornamented 
shells may be preserved.^ 

Nature works in much the same way in extracting the 
larger fossils for us from a clay. Let us climb up by the 
side of our quarry to the level ground above, where a little 
brick-yard has been opened in the Gault. Where the face 
of the cutting is fresh, the clay is stiff and sticky, and it is 
diflScult to pick the fossils out of it without breaking them. 
But at the sides of the pit the rain has long been working 
on the sloping and exposed surface, and has washed down a 
good deal of the fine material into the form of flat and 
miniature alluvial fans. The coarse-grained residue higher 
up has dried and cracked in the sun, and readily breaks up 
under our fingers. The fossils can here be got out easily, 
and often retain a handsome pearly lustre. Little mineral 
change has gone on in the shells since the day on which 
they became embedded in the mud ; the organic matter has 
decayed out of them, and they have become friable and flaky, 
while casts have been formed of their interiors by the clay 
which has hardened within them. 

These fossils include numbers of the coiled cephalopod 
shells known as Ammonites, particularly the genus HoplUes; 
and a little brown spindle-shaped body, coming to a point at 

^ See F. Chapman, *'Tbe Foraminifera of the Gault of Folkestone," Jou/rn, 
Moy, Mioroscop, Soc., 1892, and succeeding years. 



THE SURREY HILLS 267 

one end, can be found in almost any excavation. This is the 
" guard " of a small species of Belemnites; the animal was a 
cephalopod allied to the modem squids, but was furnished 
with a small straight chambered shell at its hinder end. This 
shell was protected by and sunk in a guard, popularly spoken 
of as the '* belemnite," which projected backward and was 
built of close-set fibrous crystals of calcite. The modem 
cephalopods of this type manage to do without the guard, 
or possess the merest rudiments of it and of the ancient 
chambered shell. 

The Ammonites that abound in the Gault are, like the 
Belemnites, entirely extinct; but the little bivalve Nucvla, 
which also occurs in almost every Gault section, is still a 
living genus. All through the Cretaceous system, we shall 
find this mingling of extinct and living genera, such as we 
might expect near the top of the great Mesozoic group. 

The Gault sea was of wide extent. We have no good 
evidence as to its boundaries on the north, but we know 
that it stretched right across the site of London and away 
towards Lincolnshire, passing into an iron -stained lime- 
stone in Norfolk. Up to the end of the deposition of the 
Folkestone Sands, a long- backed island or peninsula ran 
somewhat north-west and south-east across the London area. 
This old ridge has been struck again and again in well- 
borings, at about 1000 feet below the present surface. Now, 
beneath Kentish Town, and beneath Turnford on the north 
and Cross Ness on the east, the Gault clay, some 150 feet 
thick, rests directly on Triassic or Palaeozoic rocks. Here we 
have, then, an unconformable junction of a most distinct char- 
acter ; at Turnford, indeed, we pass at once from the Gault to 
Devonian shales, which are uptilted at an angle of 25°.^ 

Beneath Kentish Town, however, a patch of Middle 
Jurassic limestone is left upon the ridge, which here con- 
sists of reddish sandstone, and the Gault follows immediately 
above this. Beneath Bichmond similar beds occur, with 
10 feet of nodular sandy limestones above, which are full 
of materials derived from the Jurassic rocks. Then follows 
the Gault, which is sandy and glauconitic at the base; so 
that at Eichmond, in the specimens brought up by the 
boring- tools from depths of 1200 feet, we have written a 

^ See J. W. Judd, " On the Nature and Relations of the Jurassic Deposits 
which underlie London," Quart, Journ. Geol. Soe,, vol. xl, fig. 2, p. 760. 



268 OPEN-AIR STUDIES 

great part of the histoiy of the Surrey Hills. We can pictnre, 
first, the Jurassic sea beating upon and finally oveiHSowing 
the old sandstone coast, and depositing its wealth of sea- 
urchins and starfish and mollascan shells upon the sinking 
shore ; secondly, we see the ridge upheaved again, and the 
Jarassic coating reduced by denudation to mere banks and 
patches of white limestone, while away to the south the 
Wealden lake and rivers spread out the products of its 
decay. Then, thirdly, the sea creeps north again^ at first 
attacking the relics of the Jurassic rocks, and then protect- 
ing the remainder until our own time by the thick covering 
of Gault clay. It is by such observations, which seem slight 
in themselves, that we get an insight into what the older 
writers used to term the " revolutions of the globe." 

A boring at Chatham ^ even gives us a glimpse of the 
geography of the Wealden lake. The Weald Clay occurs 
under the Atherfield beds twelve miles to the south, but is 
absent in the Chatham section, where the Cretaceous "green- 
sands " rest directly upon Upper Jurassic clays. The border 
of the lake here was probably a muddy one, and lay somewhere 
in the limits of these twelve miles. 

How far west did the sea of the Gault stage stretch? 
We have some answer to this in eastern Devonshire. As we 
travel from Taunton to Exeter, we see on our left the wooded 
promontories of the Blackdown Hills ; and here, bared and 
brought to light, we have Cretaceous and Triassic strata in 
the same relations as those hidden away deep under London. 
The Gault beds have here overstepped (p. 219) the Upper, 
Middle, and Lower Jurassic series of Dorset, and rest upon 
the red Triassic clays. But they did not extend much f arUier 
west. We are already near the shore-line, for the fine Gault 
clays of Kent and Surrey are here represented by yellow 
glauconitic sands ; these were deposited and churned up 
again by wave-action on a coast which remained in about 
the same position from the time of the overflowing of the 
Weald to that of the Middle Chalk. The fossils of the 
Blackdown Hills are mingled in character;* but even the 
lowest Gault species are represented. 

^ W. Whitaker, "On some Boringn in Kent," Quart. Journ, OeoL Soe., 
vol. xlii, p. 30 ; and Jukes-Browne, "Historical Geology," p. 379. 

^ W. Downes, ''The Zones of the Blackdown Beds," ^rt, Joum. Geol. 
Soe,, vol xxzviii, p. 92. 



THE SURREY HILLS 269 

In our Surrey landscape, the ground rises steeply when 
we have crossed the flat of the Gault clay. The soil becomes 
at once drier and barer ; the oaks and rushes and imperfectly 
drained marshes disappear ; and we find ourselves at the foot 
of the long escarpment of the Chalk. The basement-beds 
are in many places composed of sandy limestone or calcareous 
sandstone, containing glauconite, and known as the " Upper 
Greensand " ; but this is sometimes represented by a pale 
soft clayey limestone, with abundant glauconite, so that the 
"greensand" type is only due to the occurrence of broad 
sandy reaches in a sea that had already begun elsewhere to 
deposit chalk. For us it will be sufficient to class together 
these beds and the grey marl above them as the Lower 

Chalk and Upper Greensand stage. 

The great mass known as the Chalk, often lOOO feet in 



,««(. 'Ill"*, 



^% 



'»liliUViV\V^\vA\\^\V^\^^<^\\'\\^^\%^^^^ 



Fig. 24. — AncylocercLS gigas, a oeplialopod shell from the 
Aptian stage, Cretaceous period. 



thickness, certainly merits subdivision into three stages, 
Upper, Middle, and Lower (including the "Upper Green- 
sand "). Its fossils are well known, and their occurrence in 
zones has been carefully worked out. The researches of 
French geologists, and notably of Professor Barrois, first 
called attention to the interest of our English sections ; and 
in the latest maps of the Wealden area published by the 
Geological Survey the Chalk is subdivided according to the 
fossils it contains. 

The " Upper Greensand " type of the Lower stage occurs 
often in Surrey, and forms a little escarpment of its own 
running out at the foot of the true chalk. This local step is 
a very characteristic feature of the landscape (fig. 21). The 
Upper Greensand contains a fine series of fossils, including 




270 OPEN-AIR STUDIES 

allies of the ammonites which have adopted strange fashions 
of coiling their chambered shells. The regular steady-going 
ammonites, which played so great a part in the moUuscan 
life of the Jurassic period, are now represented by forms 
coiled in a screw-like spiral, or only loosely, so that successive 
coils are not in contact. These eccentric relatives also 
made themselves prominent somewhat earlier (fig. 24), and 
herald the complete extinction of the ammonites. Perfectly 
straight forms occur in the upper beds of the Chalk ; but, 
despite this variety of type, the great group of the ammonites 
did not outlive the Cretaceous period. Nautilus, which made 
its appearance in the Trias, with allies reaching far down 
into the Palaeozoic era, has managed none the less to live on 
quietly to the present day. 

True and respectably coiled ammonites of large size occur, 
however, in the Lower Chalk (fig. 25), and are generally found 
merely in the form of internal casts. The bivalve molluscs, 
or lamellibranchs, include Pecten and true oysters, the latter 
being represented by species with extremely folded margins. 
The fauna indicates that the beds were accumulated at no 
great distance from the shore, probably at a depth not 
exceeding 50 fathoms.^ 

The Lower Chalk and Upper Greensand contain a number 
of siliceous sponges, mostly of a type known as lithistids, with 
somewhat knotty and irregular spicules; these live at the 
present day at depths of from 10 to 150 fathoms. Complete 
solution of the sponge-skeleton has often occurred, and 
marcasite may have replaced it with its brassy substance, 
weathering to a rich orange-brown. Marcasite also forms 
nodules in the Chalk, which become rolled out into the talus- 
heaps of the cliffs or quarries. These nodules have arisen by 
slow aggregation of the iron sulphide into spherical or cylin- 
drical lumps in the body of the consolidating chalk — a pro- 
cess of chemical rearrangement that is styled " concretionary 
action " (see also p. 221). The heavy nodules or concretions, 
brown on the outside, are picked up by country-people and 
are regarded as " thunderbolts," by which term meteorites are 
popularly designated. But no meteorite of this character 
has ever reached the earth, and the iron sulphide can often be 
shown to have accumulated round some fragment of a fossil 

^ Dr. W. F. Hume considers the depth may have been as great as 150 
fathomu ('' The Genesis of the Chalk,*' Proc. Oeol. Assoc,, vol. xiii, p. 222). 



THE SUEEEY HILLS 2/1 

or other solid body in the chalk. On being broken open, the 
marcasite shows a fine brassy colonr and lustre, with a radial 
stmctnre, like that of sphemlites and crystalline concretions 
in general. 

The characters of the Lower Chalk division, whether Marl 
or Greensand, show that the Cretaceoas sea was not yet 
deeper than 300 fathoms. The western shore still occurred 
somewhere away by Teignmonth and Exeter and Tannton, 
and the sea-floor was liable even to upward movements, 
whereby the Ganlt, which had already become consolidated, 
was broKen up by waves and had its fossils scattered into the 
beds of greensand. The decay of fish-bones and of materials 
rich in calcinm phosphate gives rise at the present day to 



Fia. 35. — Acanihmxrai rolkemagen»e, an Ammonite from the Lower Chalk, 



impure concretions of that material in marine deposits ; shells 
become filled np by it, and Icmpa are formed irregularly 
about them. Similarly, many of the Gault foasils became 
" phosphatic," black casts of them alone remaining, often 
enveloped in black or dark-brown nodules. These resisting 
bodies were washed out in places into the deposits of the 
Lower Chalk and Upper Greensand stage, and form a re- 
markable accumulation of rolled and " derived " material in 
the greensand beds of Cambridge. There they can be seen 
resting on a worn surface of Gaalt, an evidence of the local 
unconformity. 

As we ascend our slope in Surrey to the qnarries and the 
lime-kilns, and enter the white region of the Middle Ohalk, 



272 OPKK-ATR STCDIES 

we may fairlj ask what is the origin of the soft compact 
groand in which the larger fossils are here embedded. It has 
so uniform a character, it fills op the hollows of the fossils so 
completely, it becomes of soch extreme whiteness and parity 
in the upper levels of the chalk, that it can scarcely resnlt 
from the mere breaking up of previous limestones or of the 
shell-banks of the Cretaceous period. Something can be 
done towards its investigation by disint^Tating the rock 
gently in water, aided by a tooth-brush ; but the best way of 
observing its structure ia by making a microscopic section. 
This is quite easy (see p. 25), if the soft rock is saturated 
with Canada balsam, which has been dried and rendered 
liquid again by heating. Then we see how the body of the 
chalk is composed of minute chambered shells, or of curving 
fragments broken from them. A fine mud of similar frag- 
ments, still smaller, and of the minute oval organic bodies 
known as coccoliths, fills up the chambers and cements the 
uninjured shells. Here and there a broken piece of a 
lamellibranch, or of the spine of a sea-urchin, occupies a 
great part of the field of the microscope. K we compare 
the finer material with the calcareous oozes now forming in 
our oceans, particularly in the Atlantic,^ we shall have no 
hesitation in saying that the chalk is typically a foramini- 
feral deposit. 

It cannot, however, be regarded as necessarily a deep-sea 
ooze. For a detailed discussion of the question of the depth 
of the Chalk sea, reference must be made to Dr. Hume's 
paper on the " Genesis of the Chalk," * where the Upx)er 
Chalk is stated to have been deposited in the deepest water, 
the south-east counties of England remaining 500 fathoms 
under water from the end of the Lower Chalk age to the 
close of the Cretaceous period. Depths of 1000 to 2000 
fathoms may have occurred ; but it must be remembered that 
a broad shallow sea would fulfil most of the conditions. 
Distance from shore diminishes the abundance of many life- 
forms and the proportion of materials brought in suspension 
from the land, as distinctly as does increase of deptli ; and 
we shall see how the borders of the Cretaceous sea were 
steadily spreading northward and westward. 

' See Challenger Reports, " Deep Sea Deposits," plate xi, fig. i, and plates 
xii, xiii, and xiv. 
' Proe. OeoL Agsoe., vol. xiii (1894), p. 211. 



THE SURREY HILLS 273 

Professors Hubert and Barrois long ago called attention 
to the conglomeratic bands in the Chalk, which indicated, in 
their opinion, a disturbance of the sea-floor, its elevation so 
as to be within reach of wave-action, and the formation of 
succeeding beds from the rolled fragments of those immedi- 
ately below. The occurrences that closed the Gault age in 
Cambridgeshire appear to be repeated several times in the 
Chalk, with remarkable uniformity over wide English areas. 
Thus there is a so-called " nodular " bed, the Melhoum Rock, 
between the Lower and Middle Chalk, the irregular and 
slightly worn lumps of previous beds standing out like 
nodules or concretions on the surface of the quarries ; and 
microscopic sections will often show that there is a difference 
in texture between these derived fragments and the later 
chalk in which they are embedded.^ 

Dr. Hume 2 suggests that the alteration of currents by 
the submergence of old land-barriers, or the elevation of new 




Fig. 26. — Actinocamax plenus^ a Belemnite from the Middle Chalk ; at the left 
end there is no cavity for containing the chambered shell. 



ones, accounts for these conglomeratic bands. The associated 
fossils show no signs of shallow-water conditions, and Dr. 
Hume would regard the breaking up of the older beds as 
connected, in the case of the Melbourn Eock, with a steady 
depression rather than with elevation. A local unconformity 
in any case exists, and in South Dorset the conglomeratic 
condition occurs throughout the whole of the Middle Chalk. 

The zone of the Melbourn Eock is not merely marked by 
its structure, which would be an unsafe guide in following it 
out across the country ; but it is characterised by the occur- 
rence of a curious belemnite, Actinocamax plemis (fig. 26), 
the massive guard of which did not include the chambered 
shell of the animal, but lay beyond its posterior end, still pro- 

* J. W. Judd, "Jurassic Deposits which underlie London," Quart, Joum. 
Oeol. Soc, vol. xl, plate xxxiii, and p. 733. 

2 ** The Genesis of the Ghalk," Proc. GeoL Assoc, voL xiii, p. 229. 

S 



274 OPEN-AIR STUDIES 

tecting it from injoiy in that directioo. This prepares ds 
for later forms in which the ^ard becomes shortened, and 
for those modem ones in which it has practically disappeared. 
Sqaids destitnte of guards had, howerer, already made their 
appearance in the earliest Jurassic beds; bat t^e protected 
ones Sonrished for a long time, and did not become extinct 
until the close of the Cretaceons period. 

The Middle Chalk is a good white limestone, and sponges, 
and the little bracbiopod Terebraivia, and lamellibranchs, 
and sea-urchins, abound in it. Amoug the lamellibrancdis, 
Inoceramvs (fig. 27) is common, as it is also in the Upper 
stage; this genns often forms shells several centimetres across, 
which are corrugated with strong growth-lines on the out- 
side and smooth and slightly waved on 
the inside. These broad flat shells have 
a very flbrons structure, the calcium car- 
bonate forming little prisms perpendicular 
to their surfaces ; and consequently they 
break np very readily, and all layers of the 
Chalk, especially in the Middle and Upper 
divisions, contain fragments of Inocera- 
mus, which resemble little tiles or bricks. 
Their fibrous edges enable them, however, 
, _ easily to be identified. 

Fig. 27.— Jnoceramtu ^- ^ „ i_ . » j-. 

Caviei-i, from tbe *"!>* o^ " chert occurs often in 

Upper Chalk. the sandstones of the Lower Chalk and 

Upper Greensand stage, resembling the 
bands formed in the Hythe Beds. But it is absent in 
the limestones and marls, until we get well up into the 
Middle Chalk. Here we see characteriBtic lines of nodules, 
black when broken, and irregular in form, running along 
certain bedding-planes of the rock. A Chalk flint is typically 
white on the exterior, and is rather elongated in the direc- 
tion of the stratification. It may be more than a metre 
long, but is commonly only about 20 cm. To determine 
the origin of these lumps of chalcedony, we must carefally 
examine the face of one of the great quarries. 

The flints obviously cannot be pebbles that became 
included in the chalk at tbe time of its consolidation. 
Their outlines are far too fantastic, and they have very 
often been formed round some white sea-urchin, or round 
a fragment of Inoceramus or other lamellibranch shell. 




THE SURREY HILIS 275 

Some of the shells, moreover, have become filled with solid 
flint ; so that we begin to see that this material has in some 
way been chemically deposited. Again and again, on break- 
ing up a flint nodule, we find a hollow within, lined with 
white dusty projections; and in some fortunate cases the 
skeleton of a siliceous sponge falls out of this hollow, or 
remains in part cemented to its walls. 

Here again we have the spicular origin of flint brought 
before us. The silica may have been extracted from the 
sea by sponges, may have been redissolved, and finally may 
have concreted round other sponges or round any con- 
venient centre of deposition. Badiolarians and diatoms 
must not be forgotten as possible sources of origin for the 
silica. It appears to be a principle that concretions will 
gather most favourably round material of the same chemical 
composition ; in the same way crystals in rocks, which have 
long been at rest, may draw to themselves new material 
from their surroundings and may thus renew their growth. 
We may expect, then, that the dissolved matter of the 
scattered siliceous remains throughout the chalk will ac- 
cumulate again round undestroyed siliceous sponges. If 
these sponges form anywhere a fairly dense layer among 
the deposits, there a layer of nodular flints arises ; but this 
does not seem sufficient to account for the abundance and 
regularity of the flint bands in ordinary chalk. It is pro- 
bable that the dissolved silica went wandering in the waters 
which permeated the soft limestone for ages after its con- 
solidation, and that it finally became deposited along those 
stratification-planes which were the easiest water-ways in 
the rock. 

This is illustrated by the fact that layers of flint (" tabular 
flint ") sometimes occur in the joints and planes of fracture 
of the chalk, and in all characters resemble the nodular flints, 
except in being more sheet-like and continuous. These 
tabular flints obviously must belong to a period far later 
than that of the consolidation of the chalk ; and it is exceed- 
ingly improbable that the flints lying along the planes of 
stratification were formed at a much earlier date. 

At any rate, we may safely conclude that the flints were 
never, as some have suggested, in a lumpy gelatinous con- 
dition on the floor of the Cretaceous sea. They came 
together molecule by molecule, not thrusting aside but 



276 OPEN-AIR STUDIES 

actaallj replacing, the particles of calcareoas mnd, which 
had alivady accumnlated to form fairly consolidated layers. 
The dull whiter patches that we see in so many flints are 
regions where the sponge-remains or shells still preserve 
some of their own individuality. In sections made across 
these patches, the outlines of foraminifera, of spicules, of 
shell-fragments — in fact, all the structure of true chalk — 
can be seen as if the mass were still calcareona Some of 
the larger objects, such as pieces of Inoceramus, may remain 
unreplaced ; but the smaller shells and the limestone-mnd 
(coccoliths and broken foraminifera) have been converted 
into solid flint. The flint found in the sea-urchins or other 
shells has similarly replaced the fine chalk that originally 
filled them. Often additional flint has accumulated on the 
outside, while the shell has still remained calcareous. At 
last it may be dissolved away by comparatively modem 
percolating waters, and a perfect cast of the interior is left, 
loosely embedded in the outer mould. 

These internal casts of the heart-shaped and ovoid sea- 
urchins are very common among the stones of the flint- 
gravels, which result from the decay of the Middle and 
Upper Chalk ; and the frequent branching or simple hollows 
in many flint-pebbles in these gravels point to the material 
having accumulated round siliceous sponges. 

The extremely fantastic surfaces of many unrolled flints is 
thus explained. The silicification of the limestone has spread 
unequally in various directions, and hom-like and knotty pro- 
jections have resulted. In the old Carboniferous Limestone, 
precisely similar action is illustrated, and we can trace all 
stages between isolated nodules of flint and great uniform 
replacements of the rock over many metres of its thickness. 
In Jurassic and other limestones, oolitic structures have been 
replaced and exquisitely preserved in flint. It is quite clear, 
then, that the silica takes the place of the calcium carbonate 
during slow processes of change, and that in some limestones 
flints may still be growing. The decay of organic matter 
has possibly some chemical influence in promoting the depo- 
sition of the silica from solution, as it is believed to have 
had in the " wood opals " of various countries, in which all 
the delicate structures of tree-stems are wonderfully and 
microscopically replaced. 

The outer layer of the flints from the chalk is singularly 



THE SURREY HILLS 277 

white. The chalk itself may be washed off, and yet a 
dense white undecaying crust remains, which is seen in 
striking contrast to the black flint when we look at any 
broken specimen. Gradually, if exposed to weathering, the 
whole flint becomes dull and light-coloured ; and this crust 
is believed to be due to the fact that the flint has ceased 
to grow and spread, and is being dissolved again by the 
permeating waters. It thus becomes minutely porous, the 
opaline particles of the chalcedony disappearing first ; and 
we may compare the two parts of a common flint to obsidian 
and pumice, the one compact and almost transparent, the 
other white and opaque because of the multitude of internal 
reflections. Flints may decay away completely, if of small 
size, becoming as soft as chalk itself. I have thus written 
on a black-board with certain altered flints collected from 
a high and exposed gravel on Headley Heath ; and in the 
field they might naturally be taken for chalk. But they do 
not effervesce with acids, and are practically composed of 
pure silica ; the white crust has spread in this case through 
the whole mass of the flint pebble. 

The boundary between Middle and Upper Chalk is marked 
by a second conglomeratic band, of which a stout ovoid sea- 
urchin, Holaster plamis, is the characteristic fossil. Here we 
have, according to either theory of the origin of conglomeratic 
chalk, evidence of earth-movement, either resulting in eleva- 
tion or in the readjustment of ocean-currents ; and Dr. Hume 
quotes evidence to show that elevation actually occurred at this 
time in many areas, with a consequent increase in glauconite, 
and in materials, such as clay and small crystals, brought down 
by rivers from the land. 

But the Upper Chalk itself, in its wide distribution, im- 
plies a farther extension of the great Cretaceous sea. It will 
take us too far away from our Surrey Hills to properly discuss 
this question; but already, from "Upper Greensand" times 
onward, the sea had spread west across our islands as far as 
the highlands of Derry and Donegal, and as far north as the 
area of Mull and Ardnamurchan. The Irish conglomerates 
of quartz pebbles, and the Scotch estuarine strata, show the 
presence of land along that north-west line ; but the great 
sea, depositing pure organic limestone, now stretched east- 
ward across the whole of Europe. The old ridge under 
south-east England was finally buried deep beneath 1000 



278 OPKX-AIR fJTTDIES 

feet of marine sediments, and there were no longer traces 
of even Jurassic hills in Sarrej. Sea-nrchins abounded, 
particularly the species Anarvchytis orafus, with its flat oval 
base, Echinoeonus conietis, a steeply conical form with the 
mouth central in its base, and Mitrader eoranffuinum, a 
common heart-shaped form. These are among the very 
commonest fossils of the Upper Chalk ; and at the top comes 
a belemnite, marked by a dit in the side of the hollow which 
protected the chambered shell, the species being entitled 
Belemnitella mucronaia. This fossil is very common in the 
"White Limestone" of County Antrim, and occurs in Norfolk 
and the Isle of Wight. But in Surrey the high zone contain- 
ing it has usually been denuded away, before the deposition of 
the clays and sands which form a capping to the Downs. 

The Upper Chalk is rich in bands of nodular flints, while 
here and there a thin bed of yellow clay shows, as in the 
Middle Chalk, a temporary inflow of shore-material. In 
France and the northern parts of central Europe, a stUl 
higher chalk occurs, which may have been deposited in our 
area and then entirely lost by denudation. Certain it is that 
the tops of our Downs were greatly worn down before the 
opening of the Eocene period. Without more than a gentle 
folding, the floor of the Cretaceous sea became uplifted, and 
only sank again after hundreds of feet of chalk had been 
washed away. The flints became rolled into pebbles and 
fine sand, which went to build up the early Eocene beaches. 
Hence we must seek in France for a complete series of beds, 
marine throughout, to represent the great Cretaceous system. 
It is the old story of one set of geological observations leading 
on to comparison after comparison, until we want to travel 
round the globe to fill up all the gaps of knowledge. The 
names of the French stages, established by d'Orbigny and 
Desor, are now being generally used for the corresponding 
divisions in our own country. 

The names of the stages given on page 279 are derived from 
districts where the beds are well displayed, their origin being, 
in descending order : — ^Denmark ; the Senones, an old tribe 
near Sens, south-east of Paris ; the Turones, a tribe near Tours ; 
the Cenomani, a tribe near Le Mans, south-west of Paris ; the 
Albis, the Boman name for the River Aube ; Apt, east of 
Avignon ; Orgon, south of Avignon ; and vea xcofirj, a fanciful 
Greek version of the name of Neuch§.tel in western Switzer- 



THE SURREY HILLS 



279 



CRETACEOUS SYSTEM. 



Series, 


Stageu 


S.-B. England. 


Ireland. 


Scotland.^ 


■ 

Uppbr 
Orktaceous 


Daniaa 
Senonian 


Absent 


Absent 


Estuarine 
sands. 


Upper Chalk 


White Lime- 
stone of An- 
trim, in part 
glauconitic 


Chalk. 


Turoniaa 


Middle Chalk 


Glauconitic 
sand 

Marls and 
glauconitic 
conglomer- 
ates and 
sands 


Estuarine 
sands. 


Cenoxnaiiiaii 


r Lower Chalk. 

Upper 
t Greensand 


Estuarine 

sands. 

Beds of 

Upper 

Greensand 

type below. 


Lower 
Cretaceous* 


Albiaa 


Gault and part 

of Folkestone 

Beds 2 


Absent 


Absent. 


Aptiaa 


r Part of Folke- 
stone Beds. 
y Hythe Beds 


jf 


it 


Urgonian 

(" Barr^mian " 

of De Lappa- 

rent) 


Atherfield 
Clay 


i» 


»» 


Neocomian 

(marine) 


Wealden Beds 
(fresh-water) 


»i 


f» 



* The classification of the Scottish Cretaceous beds is taken from Professor 
Jiidd, **The Secondary Rocks of Scotland," Quart, Journ, Oed. Soe.^ vol. 
xxxiv, p. 734» &c» 

^ See J. W. Gregory, "Fossils from Great Chart in Kent," Oed. Mag., 

1895. P- '03- 



28o OPEN-AIR STUDIES 

land. The name Neocomian was formerly used for the whole 
of the stages up to the base of the Albian. The line between 
the Upper and Lower Cretaceous series is usually drawn in 
England at the base of the Gault ; but the alliance between 
the Folkestone and the Hythe beds, and the occasional uncon- 
formities between the Gault and the Cenomanian, seem to 
make the Continental custom preferable, as indicated above. 

By the removal of much of the British Cretaceous strata, 
the marine Eocene beds, when the land again sank, over- 
stepped (p. 218) various stages of the Chalk, and are found 
resting in places on Middle Chalk on the edges of the Surrey 
Downs. We learn, from following out this unconformity, 
that the North Downs, as hills, have had at least a double 
history, and that the dome across the Weald began to be 
denuded at the close of the Cretaceous period. Then it sank, 
to be covered by the pebble-beaches and clays which extend 
away to London. 

We must now finish our climb up the barren face, and 
enter the beech-woods on the summit of the ridge. Here 
we shall again and again come across patches of beautifully 
rounded flint pebbles, sometimes pure black in a matrix of 
rich brown loam, sometimes altered and bleached to a pale 
yellow in the midst of permeable sand. These are traces of 
the shore-deposits that heralded the new incursion of the sea. 
The distribution of the Eocene beds shows us that a great 
part of Britain remained above water, gulfs alone being now 
formed in the area lately occupied by the broad Cretaceous 
sea. The escarpment of the London Eocenes forms another 
ridge facing us as we walk down the dip-slope of the Chalk ; 
it draws near to Guildford on the west, and we cross it at 
Leatherhead, after which, as we return to London, it forms a 
number of clayey and hilly commons on our left. 

The flat-topped hills that stand out in the north-west 
(p. 245), such as St. George's Hill near Esher, are formed of 
the level Upper Eocene sands. Hence, like the Leith Hill 
country, they are given over to dense fir-woods, which form 
a region of singular gloom from Bagshot Heath to Aldershot. 
The yellow roads run through forests, in which every inter- 
val between the pink bare stems is occupied by farther and 
farther trees ; no light reaches the highway, except from im- 
mediately above ; and only here and there, in some sudden 
clearing, we can realise our height above the surrounding 



THE SURREY HILLS 28 I 

country, and see the sunlight gleaming on the open Downs 
to southward. 

The unconformity between the Eocene and the Cretaceous 
is not to be observed in any single quarry, the one set of beds 
lying fairly evenly on the other, and both having been sub- 
jected to the same earth-movements in recent times. But 
the solvent action of percolating water has produced striking 
appearances of local unconformity. In the great chalk-pits, 
we must have noticed how the upper layers were frequently 
traversed by wedge-like masses of brown sand, coming down 
vertically from the surface of the Downs. These are what 
the quarrymen call " pipes," and are regions where solution 
of the chalk has allowed the Cainozoic beds to fall in. The 
pipes are probably still being elongated at the present day, 
and the surface-soil above them becomes correspondingly 
depressed. Often on the back of the Chalk, particularly 
towards sunset, the light picks out circular hollows in the 
broad curvings of the fields ; in some cases these are so deep 
that the plough can no longer be driven into them, and they 
have to be abandoned to a growth of bushes, which they 
shelter and protect. These depressions are known as " swal- 
low-holes," and represent the upper ends of " pipes," their 
growth and spread being due to the underground solution of 
the chalk. 

The plane of junction between the Mesozoic and Cainozoic 
strata thus becomes very irregular. Sometimes a huge pipe 
comes down obliquely into the section formed by the quarry- 
face, and then appears as an oval mass of sand and iron- 
stained flints, in the midst of the pure white chalk. The 
workmen, requiring only the limestone, excavate round this 
mass, and finally it is left standing out as a brown buttress, 
its connexion with the surface being now revealed. 

We must not push our investigations farther towards 
London, except to note that the Eocene sea ended in an 
estuarine period, and that finally, in Miocene times, the 
British Isles generally became dry land. But the North 
Downs went under water again at the opening of the Plio- 
cene period, since some of the pipes above Lenham in Kent 
contain marine fossils of that system. A number of casts, 
in sandstone richly stained with limonite, are found included 
in the material which has been lowered into the Chalk; 
these useless lumps of "ironstone" are thrown aside by the 



282 OPEN-AIR STUDIES 

qnarrymen, and are well worth breaking np with the hammer. 
One may thus find casts of Terehratula grandis, and other 
unmistakable Lower Pliocene fossils, such as were relied on 
by Mr. Clement Reid in proving the age of these interesting 
relics.i 

Hence the Surrey Hills, in their present form, are very 
recent in their origin. If the sandy beaches of a Pliocene 
sea were spread over the denuded Eocenes, just as the latter 
had previously been laid down across the Chalk, we must 
recognise that the area, as we now know it, has undergone 
a third upheaval, practically in Post-Pliocene times. The 
Lenham pipes are now 600 feet above the sea, and traces of 
them are found at various levels on the face of the escarp- 
ment, showing that the chalk ridge has been worn back 
since they were deposited and since they were lowered by 
solution into it. Hence man himself probably existed on 
the earth before the Surrey Downs were made, and before 
the Chalk was so far cut away as to expose even the Aptian 
rocks beneath it. If we give one last look upon the land- 
scape that spreads around us from Leith Hill, the extremely 
modern character of the present features becomes impress- 
ively brought home to us. All the rich variety of scarp 
and hollow, all this freshest beauty of south-eastern England, 
seems but a trifling incident compared to the great changes 
of the past And we may picture this land of ours, in the 
next swing of the continental edge, sinking once more 
beneath the waves, and the delicately fashioned scenery of 
our own time vanishing like that which once lay around the 
Wealden lake. But, after all, our stage is not yet run out ; 
and our successors, if they lose the Surrey Hills, may be 
rewarded by the possession of still newer landscapes, and of 
still keener perceptions to enjoy them. 

If domes of strata rise out of the sea, and are carved into 
escarpments and long hollows, so also our greatest mountains 
have originated in foldings of the crust. There are surprises 
still in store for us if we again journey into Switzerland ; 
and on this occasion we will do things gently, like old-time 
travellers, and leave the train at Dole, well between the C6te 
d'Or and the Juras. Thence we will cross the hills by road, 
and so, from the Surrey Downs, attack the passes of the Alps. 

* Reid, **The Pliocene Deposits of North- Western Europe,** Nature^ vol. 
xxxiv (1886), p. 341. 



CHAPTER X 

THE FOLDS OF THE MOUNTAINS 

In the Weald we have seen how the denudation of a great 
fold has produced a considerable variety of surface, though 
the repetition of the features is clear on opposite sides of 
the anticlinal. But a series of anticlinals and synclinals, a 
series of approximately parallel earth-wrinkles, can bring scarp 
and hollow in rapid succession into the landscape ; and, if the 
slopes of the anticlinals are at various angles, the contrasts 
between one ridge and another may become sharply marked. 
In general, the term folded Strata has come to mean strata 
bent into a series of such wrinkles ; and, where the folding 
is extreme, we speak of it as contortion (Plate XI). 

In ordinary folded strata, denudation may remove the 
tops of the folds, while their bases may be hidden under- 
ground. The anticlinals and synclinals may be nipped by 
pressure in their central parts, and may expand above and 
below the region of greatest compression. Where such an 
anticlinal expands, the beds of its two halves or "limbs" 
slope outward and upward away from one another, and 
denudation may expose only this upper portion. The older 
beds are still in the centre of the fold, but the effect on the 
eye is that of a synclinal. Such an arrangement of the 
strata is frequent in the heart of mountain-areas, and is 
appropriately known as fan-Structure (fig. 28), from the 
appearance, on the bare rock-walls, of strata radiating like 
the bars of an opened fan. 

In contorted beds, the folds may become pressed over in 
one direction, so that their two limbs are parallel over long 
distances. In the sections exposed near the surface of the 
earth, it may be difficult to discover the anticlinals and 
synclinals, and the whole series looks like one limb of a 
huge denuded fold. But careful search will often reveal 
the repetition of some characteristic bed, such as a shell- 
band or a coal-seam, by which the true arrangement can 

be worked out (fig. 29). 

283 



284 OPEN-AIR STrniES 

Where one side of an anticlinal or a synclinal comes 
thus to lie npon the other, we may call the whole a 



FiQ. aS.— Section iij.rsTRATrso pAS-STBrcrrBK ni * 

MorsTAra-CH.vra. 

The (totted liDex fibow Ibe ori^nal anticUoala mh) BynclinalB, 

now worn down bj denudation. 

recmnbent fold; and it is clear that in the nnder limb 
of sDch ao anticlinal the beds follow one another in a 




Fig. 39.— Section illustbateio Rbfetitiox o 
RcccMSBKT Folds, as bibn in ASCBSDisa 

In the anticliiuila t and 3 tlie strata lU-e rerenad in the lower limbe of the folds ; 
in the gynclinala a and 4 the reiersal is in the upper Umbe. Such toldiDg is 
usn&llj complicated in nature bj thnut-planefl. 



reversed order, the older ones resting upon the younger. 
In the case of a recnmbent syncUnal, the reversal 



THE FOLDS OF THE MOUNTAINS 285 

takes place in the npper flank of the fold. (See figs. 29 
and 33.) 

These are only some of the difficulties that geologists 
encounter in dealing with strata which have been subjected 
to considerable earth-movements. The whole mass often 
gives way along a certain plane of fracture, frequently by 
the rupture of a fold, and the beds on one side of the plane 
slip up, while those on the other side slip down, the effect 
being what is called a fault (fig. 30). The amount of 
shifting away of a bed from its normal position, due to 
faulting, may vary from two inches or so to perhaps two 
miles. The connexion between faults and folds is often 
seen by the strata being bent np towards the plane of frac- 




ture on the side that has been lowered, or on the downthrow 
side, and down towards it on the opposite, or upthrow side. 

A fault, as we may see it in horizontal beds in a Surrey 
chalk-pit, or in one of the red clay-pits of the Midlands, 
presents no especial difficulties ; but faults, when we cannot 
see them in section, may puzzle us by producing a repetition 
of the beds upon the surface. A fault along the strike of 
uptilted beds causes a part of the aeries to begin over again, 
with a corresponding repetition of the scenery to which it 
gives rise ; and a fault more or less parallel to the dip 
carries the inclined beds forward on the side that has been 
dropped, so that their outcrops end off abruptly against the 
fault-plane, and their continuation has to be sought for at 



286 OFEN-AIR STUDIES 

some distance away along that plaue (fig. 31). In looking 
at a geological map, this laieral shift can often be observed 
(the faults in English maps are represented by white lines) ; 
and the side on which the beds lie at the lower level can be 
determined by the following rule : — 

In tilted strata, all faults, except those parallel with the 
strike, cause a lateral shifting of the outcrops, and thus older 
and younger strata are brought into contact at the fault- 
plane ; the side on which the younger stratum of any pair 
lies is that on which the beds lie at the lower level. This is, 
therefore, the downthrow side of the fault. 

But when faults cut one another, like successive igneous 
veins, complications rapidly ensue ; and a series of faults of 
different ages, occurring in con- 
torted strata, produces repetitions 
and mysterious displacements that 
tax the most experienced surveyor. 
In the stress of great earth-pres- 
sures, even recumbent faults occur, 
colled tbrast-planea, along which 
masses of strata may be moved for 
several miles, and may be left 
F1Q.31.— PlanofaFaultin stranded on the top of materials 
iNULiNBD sthati, AH 8BBN ^f ^jj utterly incongruouB character. 

UPON A GeoLOQICAJ, MAP. mi i i . .1 

1 h rust-plane 8 can convert the most 
arrow pom e epo innocent and conformable folded 

towards which tbe beds dip. ■ ■ , _r . rti.- 1 

D and u Ha in Hg. 30. senes into a perfect Uhinese puzzle 

of dislocated parts ; the tops of anti- 
clinols may be brought directly over the bases of synclinals, 
an oval grouping of strata being the result, while horizontal 
beds are often caused to lie upon vertical ones, with an 
appearance of striking unconformity. Yet in this latter 
case the two discordant series may be in reality one and 
the same, the horizontal top of some broad anticlinal having 
been carried forward on the thrust^plane until it rests above 
the vertical beds of one of its own limbs. 

One puzzling effect of gently sloping thrust-planes is to 
bring up strata from the depths and to laud them on those 
that are much younger. To see what the field-surveyor has 
to face, it is well to draw imaginary contortions with chalk 
upon a piece of brown paper ; then cut the whole across 
along an approximately horizontal line, and shift the one 




THE FOLDS OF THE MOUNTAINS 287 

half over the other, noting the great variety of apparent 
unconformities produced, according to the extent of the 
movement. An ecstasy of confusion can be reached by 
drawing a contorted series in which true unconformities and 
ordinary faults already exist, and then dividing that by a 
great thrust-plane. One may imagine the joy with which 
well-marked fossil zones are hailed in a country where 
the structural features have obliterated in this way all the 
original relations of the strata. 

Thrust-planes very often occur through the heart of a 
recumbent fold, the opposite limbs of the fold becoming drawn 
far away from one another along the plane of fracture. 

In all varieties of faulting, we have no evidence of rapid 
action in the tearing and displacement of the beds, but 
rather of long slowly acting pressures, which at last could 
not be resisted, the rocks yielding gradually, and.shifting 
their places year by year. A number of sudden little slips, 
however, probably occur during such movement, a shock 
being given at each slip to the beds on either side. Some 
one has hence aptly described faults as "fossil earthquakes." 

Often a broken and mingled mass of rock occurs along 
the plane of fracture, its angular fragments being derived 
from all the rocks affected by the movement. This broken 
material is the fault-rock or fault-breccia.^ We must re- 
member that most rocks in a contorted series cannot break 
up, since their parts are under such pressures, exerted all 
round them, that they have no room in which to slide apart. 
But sometimes there are masses of a compressible or yielding 
character lying between harder and more resisting ones; 
then the former series begins to be deformed, and to flow in 
a direction perpendicular to that in which the main pressure 
is exerted ; and this allows the harder but more brittle masses 
to break up, so that they are pressed in fragments into their 
softer neighbours. A breccia results, of all degrees of coarse- 
ness ; and we have often to trace it to some distance before 
we can determine its true character. Thus, on the pro- 
montory of Howth near Dublin, hard quartz rocks have 
been crushed and broken among the shales, with which 
they once formed a conformably bedded series. When an 

^ Pronounced bretshia, the word being Italian, and having been originally 
applied to a number of ornamental stones composed of angular fragments set 
in a natural cement. 



288 OPEN-AIR STUDIES 

igneous mass thus becomes ** brecciated " under earth-move- 
ments, it may easily be mistaken for a volcanic tufif. 

The flow of yielding beds to escape from pressure is 
illustrated in many common outcrops of tilted strata. An 
immense number of small cracks are seen in the beds, run- 
ning perpendicular to the strike, and perhaps rendered con- 
spicuous by an infilling of quartz or calcite. These cracks 
result from the oozing away of the beds under the pressure 
which has produced their tUting. 

Armed with these ideas, we may now set out upon our 
next and longest journey. We have crossed the Paris 
Basin, which is so like the broad synclinal area of London, 
with the Cretaceous beds fringing it, their escarpments 
facing outwards in a ring; we have climbed to the very 
sources of the northern rivers, and have seen the Seine and 
the Mame diminishing on the great Jurassic plateau ; and 
now we are down from the Cote d'Or, across that escarpment 
also, and ready to attack the folds of the long blue Juras and 
the Alps. 

The great ridge behind us, worn out of the Middle Jurassic 
limestones, forms one flank of a valley fifty miles wide, the 
other flank being found in the Jura range about Poligny. 
The Saone, descending from the Vosges, and its tributary 
the Doubs, almost parallel to it, here unite to form a river 
worthy of such a valley. Beneath and beyond their modem 
alluvial reaches, the whole wide hollow is covered with a 
plain of Pliocene gravels, which choked the original valley 
soon after it was excavated. Paludina, the common fresh- 
water gastropod, occurs in some of the associated marls, and 
the bones of extinct elephants, Elephas meridionalis and 
antiquus, indicate the age of the deposit. The valley, 
then, is somewhat older than our Wealden excavation, and 
was filled with gravel from the Jurassic slopes round it in 
Upper Pliocene times. 

From Dijon, at the foot of the C8te d'Or escarpment, to 
Auxonne, the ground is practically level ; but just before the 
quaint old town of D81e we come over the shoulder of a gentle 
hill. To the north there rises a broad-backed ridge, some ten 
miles long, which forms a barrier between the Rivers Sa6ne and 
Doubs. The rocks composing it are folded masses of Triassic 
and Permian strata, resting on granites and " gneisses," which 
are at least older than the Carboniferous period. This little 



THE FOLDS OF THE MOUNTAINS 289 

boss of Dole is a model, as it were, of the great forest-range 
of the Vosges farther to the north, and is by far the most 
interesting object in the valley. On its flanks Jurassic rocks 
were deposited, which form the hilly ground on which D61e 
itself is built ; but the great stretch of Pliocene gravels has 
hidden almost all these older features. The D61e ridge is in 
reality a projecting peak of a buried continuation of the 
Vosges ; it is a survivor of a mountain -range older than 
Jurassic times, and in part older than the Carboniferous 
period ; and it speaks to us of a European continent which 
passed away almost completely beneath the Jurassic sea. 
Doubtless, between D61e and the central plateau of Auvergne 
(p. 148), other peaks approach the present surface; and we 
shall soon see how these buried mountains have asserted 
themselves in resisting more recent earth-movements. 

After the steep streets of D61e, we have another fifteen 
miles of extremely level country, across the old gravels and 
the later alluvium of the Doubs ; but a few rolls of hills soon 
begin to rise up against us, and at Mouchard we pass under 
a railway-arch and are suddenly in a new world. The rail- 
way clings to the skirts of the mountains, which here rise 
quickly from the plain. The unconformity between the 
gravels and the Juras is as marked as that between the great 
plains of India and the Himalayas, and the change of scenery 
is equally abrupt. We are now among the masses which 
have showered down all these limestone pebbles into the 
valley. The road begins to climb in windings to the head 
of a long combe; the streams flow down swiftly under fir- 
woods and great limestone scars; and the side-valleys are 
flanked by bold cliffs and craggy promontories, on which the 
fortresses of the frontier are set proudly, tier on tier. If 
Auxonne is a typical city of the plain, Salins, on the other 
hand, massed upon a cliff-set slope, is typical as a mountain- 
stronghold. Mile by mile we push up into the forest, meeting 
cows with bells about their necks, driven by peasant-girls, 
and enormous timber descending on carts drawn by oxen, 
and all the life of a highland roadway under the clear cool 
mountain-air. We are now well up among the Juras, which 
stretch to the north-east beyond B8.1e, and on the south to 
Chamb^ry, a range of 200 miles. 

Travellers by rail into Switzerland also know well this 
sudden transition from the gentle lowlands to the Juras. 



290 OPEN-AIR STUDIES 

Even on the route to Bale, where we climb somewhat mildly 
at the first, we wake up after the long night-journey, to see the 
clouds wandering among crags and pinnacles, and the rivers 
foaming in limestone canons far below. The long escarp- 
ments are here far bolder things than in our homely and 
simple Surrey hills. The dip-slopes are often as steep as the 
scarped fronts, and the frequent folds cause them to face 
now this way, now that, in the complexities of the same 
mountain-landscape. The valleys are cut deeply into the 
pale grey rock, which often rises in characteristic vertical 
walls, like those of the Cheddar gorge in Somerset ; and 
these irregular canons form the defiles known locally as 
cluses. Occasionally some wider valley-floor thrusts back the 
fir-woods on either hand, and its soil is given over to cultiva- 
tion. The villages, which die away in the cluses, are here 
grouped close to one another along the road, six or seven 
being in view at once. Clearly some attraction beside the 
Jura limestone has drawn these agriculturists together. 

After the broad grassy uplands of Pontarlier, where we are 
on the real crest of the mountains, with the ridges only feebly 
emerging round us, we enter another defile and cross the 
frontier into Switzerland. The descent of the Jura is far 
severer than the western ascent; but the steep valleys are 
broken here and there by some oval alluvial area, the floor 
of an old mountain-lake. The busy little towns, alive with 
mechanical industries, take advantage of these level patches ; 
and in between them the road may have to be cut in the 
side of sheer limestone cliffs, to secure a passage from one 
town to another. Far below, we may see the old mule-track, 
struggling with the torrent for a place in the floor of the 
ravine. As we come down on Neuchgltel, another huge valley, 
like that of the SaSne, opens before us, with blue lakes lying 
in it. One flank is formed by the Jura mountains, but the 
other is still more magnificent ; for we see there, twenty miles 
away, the blue-grey foot-hills of the Alps, with the snow- 
masses of the central range, thrice as distant, towering, like 
sunlit clouds, beyond. This first glimpse of the Alps is 
one of the most impressive features of our journey. While 
we are pausing among the clififs and forests of the Juras, 
we know that their mightier rivals wait for us across the 
lowland. When we finally approach them, we shall be lost 
in the complexities and indentations of their denuded sur- 



THE FOLDS OF THE MOUNTAINS 



291 



face ; but here, as at Schafifhausen and other distant view- 
points, we can grasp all their grandeur as a massive and 
continuous mountain-range. 

The Juras are built almost entirely of Jurassic strata, 
consisting mainly of massive and pale grey limestones ; and 
their folds have considerable regularity, striking north and 
south from Chamb^ry to Geneva, and then gradually curving 
round, until at BSIe they strike E.N.E. It very often 
happens in denuded areas that ridges are carved out of the 
heart of synclinals, because the beds in them have become 
pressed together and made more resisting; while the anti- 
clinals, on the other hand,, give way along their crests, pro- 
ducing valleys running parallel to the strike. But in the 



Schonenberg 



Probstberg 



ITaffon 



Batsthal 




1000 SOO 

1 I I I I * 



1000 



Scate of Metres 

Fig. 32.— Ridges and Valleys formed by Folds in the Jura Mountains. 

E, Eocene lacustrine deposits ; M, Middle Jurassic ; R, recent deposits ; 
U, Upper Jurassic. (After Rollier, " Livret-guide g^ologique," pi. iii.) 



more gently folded regions of the Jura, where faults and 
reversals of strata have not complicated matters, there are 
long ridges formed by anticlinals, and valleys lying in syn- 
clinal hollows ; so that the general structure of the range 
has always been referred to as one of unusually simple and 
diagrammatic character {^^, 32). Faults and reversals, 
however, occur, approaching those of the Alps themselves in 
disguising the true relations of the strata ; ^ and the total 
chain now occupies only two-thirds of the space that its 
strata covered before the folding-processes came into play. 

Cretaceous beds are found in the Juras ; but, with a few 
exceptions on the west, only the lower series appears to 

^ See Bertrand, BvR, Soc. g4ol, de Fra/nce, 3me. s^r., tome x, p. 119. 




292 OPEN-AIR STUDIES 

have been deposited ; hence we conclude that an upheaval 
occurred along this line abont the middle of the Cretaceous 
period. But the valleys along which so many of the villages 
cluster are floored with fresh-water Eocene and estuarine 
Oligocene beds, oysters occurring in the latter. The sea was 
not completely thrust out of the area in Lower Oligocene 
times ; and north-west of Solothum we find traces of marine 
incursions even among Miocene strata.^ The Miocene of 
the Juras is in general fresh-water; but the deposits are 
folded, and are preserved along the synclinals of Jurassic 
rocks. Hence the great and final squeezing of the Juras to 
form a mountain-range occurred as recently as the end of 
the Miocene period. Prior to that, a promontory rose here, 
bordered by scattered islets ; and in early Cretaceous times 
scarcely a rock had appeared above the sea 

The form of the range as a whole must have a meaning ; 
and here our minds go back to Dole, with the little boss of 
ancient crystalline rocks appearing above the surface of the 
plain. If we carry on the line of this ridge to meet the 
Vosges, we see that the old axis of the Vosges-Dole moun- 
tains ran parallel to that part of the Juras which lies to the 
south-east. Beyond Bale, the similarly old granite mass of 
the Black Forest forms another landmark of the ancient 
floor of Europe ; and it is just against this region that the 
Jnras begin to swing round to the east. Turning to the 
other end of the chain, we see that west of it, across the 
alluvium of the Saone, the central core of France sends out 
long ridges to the north, parallel to the adjacent Juras. It 
now seems certain that the earth-movements which com- 
pressed the chain exerted pressure from the south-east ; the 
upper layers of the crust became wrinkled up, but the far 
older mountains of Europe acted as buttresses to resist the 
movement. Forced against the hidden slopes of the central 
plateau of France, against the ridge of Dole, extending to 
the Vosges, and against the stubborn highland of the Black 
Forest, the whole chain assumed a crescentic form, its concave 
side being towards the direction from which the pressure 
came. We thus gain a fine conception of the sliding of the 
Mesozoic beds over a land-surface which had long been buried, 
which they had been unconformably laid down ; and 

▼ret-guide dans le Jura et lea Alpes," CongHs gicl, international^ 
3. 



THE FOLDS OF THE MOUNTAINS 293 

we see that, because the ancient ranges had run from the 
south to the north-east and east, our far later Juras were 
forced to take up the same curve. 

We must now pass out from Neuchatel, with its cuttings 
in the yellow Neocomians, and ascend the valley of the Aare. 
We cross a somewhat irregalar lowland, cumbered with 
materials brought down by rivers and glaciers in recent 
times, and rise from Berne into the true foot-hills of the Alps. 
Bound us are wooded knolls, as large as British mountains, 
formed of upturned Miocene and Oligocene strata ; some of 
the Miocene beds are marine, and yet they are clearly in- 
volved in the movements that have made the Alps. 

Huge banks of conglomerate occur in the Miocenes as we 
near the central range. The bedding is sometimes shown by 
the arrangement of the pebbles, and we see these old delta- 
cones and alluvial flood-banks now pressed together and 
folded, and sometimes absolutely vertical. The blue clays 
of the Miocene sea, with a wealth of moUuscan shells, are 
abruptly overlain in places by these thick conglomerates. 
A fine study may be made of them away in the north- 
east, close above the town of St. Gallen. Here the earth- 
movements have crushed the pebbles into one another, the 
limestone pebbles becoming dissolved under the stress, and 
receiving perfect impressions from those forced into their 
surfaces. Everythiug speaks of the greatest earth-movement 
and pressure ; and yet these beds were contorted as recently 
as the Pliocene period. 

But a mountain-range must have existed near at hand to 
supply the abundant pebbles. Near Thun, as we reach the 
first lake on the Aare, we find pebbles of limestone, worn 
from the Cretaceous and Jurassic rocks, forming whole banks 
of the conglomerate. With them are pebbles of granite and 
other crystalline rocks, such as we shall study in the central 
ridges; so that these older masses had in part become un- 
covered and denuded in Miocene times. The conglomerates, 
indeed, represent a period when something like the Alps 
existed to the south, but when the Mesozoic limestones 
occupied a much larger area on the surface than they do 
at present. 

Farther on, as the road is cut and tunneled in pale yellow 
limestone above the Lake of Thun, we find fossiliferous beds 
full of large f oraminif era, the genera Nummulites and Orhitoides 



294 OPEN-AIR STUDIES 

being predominant. These are Eocene marine beds, the so- 
called " Nummulitic strata" of the Alps. They have a strangely 
massive and compacted air when compared with our gently 
dipping clays and sands of the same age in south-eastern 
England (p. 280). 

Eibs and ridges of Cretaceous and Jurassic limestones, 
grey and pale as in the Juras, now appear from under the folded 
Eocene ; and at Interlaken, between the Lakes of Thun and 
Brienz, we have left the Cainozoic foot-hills, and find the 
Mesozoic rocks, crushed and bent and reversed in order, 
against the huge wall of the Bernese Oberland. 

We are now in the country of the lakes, with that of 
Lucerne temptingly in the north-east, and the great Lake 
of Geneva in the south-west. Following the strike of the 
strata in the foot-hills, we cross the Brunig Pass, which is 
merely a notch caused by the cutting back of the head of 
a northern river into the wall of the valley of the Aare. As 
we descend towards the Lake of Lucerne, we have Eocene 
and Oligocene masses piled 4000 feet above us on the left, 
and Eocene and Jurassic beds alike infolded towards the 
summit of the Titlis, 10,000 feet above the sea upon our 
right. The later earth-movements, then, have clearly re- 
sulted in serious mountain-building. 

The lakes themselves may claim our attention for a time. 
What connexion have they with the general structure of the 
foot-hills ? The Lake of Thun may have accumulated behind 
the great alluvial banks which choke the valley from Thun to 
Bern ; and the flat between this lake and that of Brienz is 
clearly formed by the encroachment of a delta due to torrents 
coming from the south. But the depth of the floor of these 
lakes would probably suggest additional causes of their for- 
mation. When we reach the Lake of Lucerne, with its 
singular winding form and its long inlets, we are irresistibly 
reminded of our west-coast fjords. The valley that we de- 
scend from Samen is continued by one of these inlets; to 
the west, the Eeuss issues along another ; and the lake 
stretching up to Kussnacht seems to have occupied the 
whole of a valley-floor. A rise of 80 feet in the waters of 
the lake would extend it up another valley from Brunnen 
towards Schwyz, and would connect it across the low col with 
the Lakes of Lowerz and Zug. 

The grandest portion -of the Lake of Lucerne is from 



i 



THE FOLDS OF THE MOUNTAINS 29 S 

Brunnen south towards Altdorf, where the walls come down 
almost vertically into the water, while the railway finds room 
only by tunneling, and the road climbs high above, cut into 
the face of the cliff. It is a repetition of the steep features 
of the north shore of the Lake of Thun. Surely here we have 
a flooded valley, with a plain of alluvium forming beneath the 
water in its floor (compare pp. 81 and 141). 

The depth of the lake in places reaches 850 feet, that of 
the Lake of Zug being 1320 feet ; in neither case can a vast 
alluvial dam be pointed to as the cause of this great accumu- 
lation of the waters. The Reuss runs out at Lucerne through 
a narrow groove cut in Miocene hills ; but no river can have 
excavated the deep and narrow bed of the lake, as we now 
know it, between Lucerne and Altdorf. Yet the whole 
plan of the lake is clearly connected with the rivers ; the 
explanation must be that the Alpine movements continued 
even after the Reuss had carved its channel, and that the 
floor of the valley became bent, either by an uptilt near 
Lucerne, or by a subsidence of its central and upper por- 
tions. Considering the length of the lake, some twenty-four 
miles, a small angle of earth-movement would suffice to give 
it considerable depth. 

It is now believed that the Swiss lakes as a whole result 
from the formation of local depressions, and partly from a 
sinking of the central Alpine chain,^ which here and there 
has actually reversed the direction of the slope of valley- 
floors in certain regions. The great Lake of Geneva, which 
is similarly a feature of the foot-hills, is thirty-seven miles long, 
and 1 014 feet (309 metres) deep. The detrital cone of the 
Rhone goes down steeply under the water, much like an 
alluvial cone on a mountain- side ; but the steady flow of the 
river washes out the finest material, and spreads it with re- 
markable evenness over the central floor.^ The original hollow 
formed by earth-movement was evidently much deeper, and 
is being filled up by an extraordinarily uniform and level 
alluvial flat. 

The formation of lake-basins through the occurrence of 
movement in the floors of valleys has gone on equally on the 
broad surfaces of continents, as in the case of the inland 

^ Forel, "Le L^man," tome i, p. 231 ; ffevnif "Die Enstehung der alpinen 
Randseen," Vierteljahrschr. natv/rforsch, Gesell, Zurich, Bd. xxxix (1894), p. 81. 
^ Forel, "Le Ldman," tome i, p. 51. 



296 OPEN-AIR STUDIES 

seas of North America, and among the narrow grooves of 
mountains, as in our Scottish highlands. Loch Ness is thus 
a flooded portion of the Great Glen, 20 miles long, i J miles 
wide, and 774 feet in depth. 

Hence the lake-region brings the period of folding in 
the Alps very near to our own time ; and occasional earth- 
quakes, particularly at the Venetian and Croatian end of 
the chain, point to the actual continuance of movement, 
upward or downward, at the present day. These mountains, 
then, which began their great uplift through the waters of the 
Eocene sea, are not even now in a state of equilibrium and rest. 

The upper half of the Lake of Lucerne lies among the 
folds of Cretaceous strata, which are superbly seen upon 
the mountain-walls that bound it. The Upper Cretaceous 
series is here present, showing that the Alps did not share 
in the early upward movement which made the Juras a 
promontory in the Cretaceous sea. The Miocene con- 
glomerates have been carried up and contorted to form 
the summit of the Eigi, S906 feet above the sea; and in 
the valley at Altdorf the nummulitic Eocenes have become 
bent in under the Lower Cretaceous beds, a fine example of 
reversal. As we commence the ascent of the St. Gotthard 
Pass, these marine Eocenes lie caught in above us on the 
peaks of the Windgalle (fig. 33), forming a long recumbent 
synclinal; Jurassic strata wrap round them, and tower in 
crags above them in the reversed upper limb of the fold. 
This is the last we shall see of the Cainozoic beds on this 
side ; for we are now on the threshold of the crystalline 
masses which compose the central Alps. 

The contrast between these and the Jurassic and Triassic 
beds, which are thrust across their upturned edges, is at first 
of the most unmistakable character ; but we must be on the 
look-out for synclinals of the Mesozoic rocks folded deeply 
into the heart of the chain. The junction is no longer 
merely an unconformable one, but is complicated by the 
fact that the Mesozoic sediments and the underlying crystal- 
line rocks have all been involved together in the greatest 
earth-movements of the Alps. The eroded coast of Mesozoic 
times, the sands and muds and limestones formed against 
it, and the sea-floor on which they lay, have all been rolled 
up as if they were a mere film upon the surface of the earth. 
It is as if we were to lay down two or three thicknesses of 



THE FOLDS OF THE MOUNTAINS 



297 



carpet to cover np the irregularities in the floor of some 
old cathedral, while changes in its level still go on. At one 
point the supporting arches of the crypt give way, at another 
the columns remain firm ; and finally the floor becomes bent 
and broken, the carpets, and the layers of dust upon them, 
rising and falling on its folds. The crypt thns represents 
the unknown masaee of the inner cmst; the floor is the 



Ma derancrthsl 




', Carboniferous, repeated also uniier tbe letterL; E, Eocetie ; G, Goeiiifi; 
J, Jumseic ; L, Lavixs of Carboniferous age ; S, Scbista. (After Heim and 
Schmidt, "LiTret-gu[deg&)1ogique,"p1. viij.) 



ancient crystalline ground of Europe ; tbe carpets will serve 
for the Mesozoic sediments, and the dust upon the topmost 
for the Eocene and later accumulations,^ 

The rocks that we now meet with in climbing the 
central range have mostly a distinct structure, formed by 
alternating layers of different crystalline minerals. Some 

' FrofuBsor Suess, in hia "Antlitz der Erde," renders tha above cum- 
parieon not so fnnciful as it may appear, by ui^ing that subBidenoe of the 
crust leaves mountain-moeaes standing up, wherever older pillars and ridges 
support tlicm, like our cr^pt-columne, from below. But subsidence of the sur- 
ri>unding areas, acting alone, will hardly account for the enornious amount of 
thrusting and contortion observable in great mountain-chains. 



298 OPEX-AIR STCDIES 

of these rocks suggest the altered material in contact with 
the granite of onr highland (p. 199); while others are far 
more coarse-grained, and show large crystals of quartz and 
felspar. The more finely grained varieties can be split 
parallel to the planes along which the minerals have de- 
veloped, and derive their name from the Greek axi^ta, "I 
cleave/' being known as SchistS. The coarser and more 
felspathic types are known by the old Saxon mining term. 

Gneiss. 

It is obvions that their constituents have not been 
deposited in layers by ordinary sedimentary action. They 
are intergrown with one another, and here and there radial 
ing tufts of some rod-like mineral shoot out along the 
layers. Mica, dark or pale, is one of the very commonest 
constituents, often covering whole curving surfaces of the 
rock ; quartz occurs in streaks and elongated nodules ; and 
little red garnets may be seen, with the micas folded over 
them, as if they had been pressed against an obstacle. 

All these features are still more marked under the 
microscope, if the section is cut across the layers. Com- 
parison with our specimens from the contact of shale and 
granite (p. 200) shows that we are again dealing with a 
secondary mineralisation. The original condition of a schist 
is, however, very hard to trace, owing to the complete 
crystallisation that has gone on in its materials. It was 
formerly believed that new minerals had developed along 
the original planes of bedding ; but it appears that the 
schist-planes generally arise during the alteration of the 
mass, and obliterate any structure which it may formerly 
have possessed. Schists and gneisses represent, indeed, the 
higher stages of metamorphism (p. 199). 

Slate serves well as an example of a rock in which new 
divisional planes have arisen under metamorphic action. 
The beautifully marked bedding of shale (p. 100) is due to 
the tiny clay particles having all become laid out with their 
longer axes in parallel planes, like little plates spread in 
layers over one another. The weight of subsequent beds 
presses any upstanding particles down into the requisite 
position, thereby assisting the delicate regularity of the 
stratification. The rock thus splits, almost like sheets of 
paper, along its planes of bedding. But if such a rock is 
subjected to steady pressure, acting parallel or obliquely to 



THE FOLDS OF THE MOUNTAINS 299 

the bedding-planes, the little platy particles will shift among 
themselves, and will finally struggle round, until their flat 
surfaces are perpendicular to the direction of pressure. The 
delicate shale-structure thus disappears, and still more marked 
planes of division arise in a new direction throughout the 
rock. We then say that it possesses a cleavage, which is 
one of the earliest features of metamorphism produced by 
pressure. 

Again and again we can trace in slates the direction of 
the original bedding. Greenish bands run across the cleavage- 
surfaces, and are often somewhat crumpled. These represent 
gritty and more resisting beds, which were unable to take up 
the cleavage. It is clear that cleavage could be produced in 
an irregularly piled mass of plates, or in a sackful of pins ; 
but it could not arise in a mass of well-rounded sand. The 
particles must be distinctly short in two directions and long 
in the third, as in the case of rod-shaped amphiboles, or long 
in two directions and short in the third, as in the case of 
flakes of mica. Grains of spherical form are obviously not 
forced to shift their positions in this way under pressure. 

The chances are that a rock-mass, subjected to such 
enormous pressures as occur within the earth, will tend to 
become deformed, and will flow away in the direction of least 
resistance (compare p. 288). Usually, as we have said, a 
movement will be set up among the particles in directions 
perpendicular to that along which the pressure acts. If there 
is space for such movement, the more resisting particles may 
become fractured, and their powder may be streaked out 
round about them. Thus sand-grains may be converted into 
lens-shaped masses of powdered quartz, the principal cracks 
that cross the rock being parallel to the direction of pres- 
sure.^ By this spreading out and deformation of the original 
grains, even a sandstone may have a rude cleavage imparted 
to it. 

In almost every slate, chemical and mineral changes have 
accompanied the purely physical ones. The cleavage-surfaces 
become coated with delicate films of mica, and this mineral 
developes abundantly through the rock. But its plates can 
grow only in the direction of the cleavage-planes, and thus 

^ See W. J. Sollas, " On the Structure and Origin of the Quartzite Rocks 
in the Neighbourhood of Dublin," proc. Boy. Dublin Soc., vol. vii (1892), 
p. 185. 



300 OPEN-AIR STUDIES 

finally help to emphasise these surfaces of division. When 
new minerals have developed to a conspicuous extent, the 
rock passes into a schist. A simple slate is merely derived ; 
a schist possesses a cleavage, accompanied by more or less 
extensive molecular changes, its older constituents becoming 
enlarged by the addition of new crystalline material, and new 
combinations occurring, giving rise to " secondary " minerals. 

The mineralisation of the rock, however, destroys the 
perfection of the cleavage. Knots of garnet, quartz, or 
andalusite, needles of amphibole, and thick lens-like aggre- 
gates of mica, grow under the influence of heat and pressure, 
and roughen the surfaces of division. Let us picture the 
results of lateral movement among all these materials, whether 
they have already consolidated or are still developing. The 
rock tends to ooze outwards in directions perpendicular to 
that of the pressure. Every mineral aggregation becomes 
deformed and spreads out into a lenticle ; even the quartz 
may yield, as we saw above, and the robust garnets may also 
be broken down. There will thus be a true flow of the 
ciystalline materials, the micas especially being carried along 
in sheets over the more knotty and irregular constituents. 
Silvery mica becomes, in fact, often plastered on to the sur- 
faces of every other mineral, and assumes an exaggerated 
importance until we break the rock across the cleavage-planes. 
These planes are so wavy and irregular, so modified by the 
flow of the mixed materials, that we cease to speak of 
" cleavage " in a schist ; we say that the rock possesses 
foliatioiL The " folia " which give rise to this structure are 
the deformed and flattened minerals, their typical shape being 
that of greatly extended double-convex lenses, often bent 
and crumpled. The thickest portion of any one may be taken 
to represent the region where the crystal or crystal-group first 
began to develope in the rock. 

After what we saw of contact-metamorphism (p. 199), we 
shall not be surprised at the variety of minerals that arise 
during these larger processes. Felspar granules are common, 
and form a sort of mosaic in certain layers ; and long needles 
of green hornblende, or of various silicates rich in alumina, 
spread aloug the planes of foliation. There is a complete 
passage between slate and schist, and between schist and 
certain types of gneiss, and the one rock may have arisen 
from the other by long-continued metamorphism. 



THE FOLDS OF THE MOUNTAINS 301 

But it is only rarely that crystalline schist's can be traced 
in the field into the sedimentary rocks which provided their 
materials. The folding and faulting of the whole rock- 
masses have been so enormous that all continuity between 
the original unaltered sediment and the metamorphic product 
is likely to have been broken through. Moreover, schists 
very commonly arise from the metamorphism of igneous 
masses, in which a number of minerals are present ready- 
formed, serving as centres for new products to gather round. 
Thus augite-diorites have been traced into hornblende-schists. 
The pyroxene breaks down and recrystallises as granular horn- 
blende; the plagioclases become reconstituted in fine-grained 
and similarly granular groups ; and the flow of the rock under 
pressure draws out these minerals into distinct foliated bands. 
Every feature of the flow-structure of molten lava (p. 165) is 
imitated by the movement of these crystalline and practically 
solid materials. The larger crystals of the original rock often 
escape complete destruction, and appear as elongated knots or 
" eyes," disturbing the regularity of the foliation. 

Similarly, a great proportion of the gneisses result from 
earth-pressures acting on granites and their allies. The rock 
breaks down ^ and begins to flow ; the quartz in part becomes 
powdered, and the larger grains are cracked and elongated ; 
the felspars are similarly broken and deformed ; and a folia- 
tion is given to the mass by the mica or other yielding sili- 
cate, which forms films and wavy streaks in among the other 
minerals. It may be that some gneisses show merely the 
original flow of the molten rock (p. 212), particularly where 
the mass was intruded after a certain amount of separation 
had gone on among its constituents.^ In other cases, the in- 
trusion of parallel igneous sheets along the divisional planes of 
some crystalline rock has given rise to a coarse gneissic struc- 
ture, the bands of the original rock alternating with those 
formed by its invader. But, in the great number of gneisses, 
there is clear evidence of the influence of pressure-meta- 
morphism. The varieties of schist and gneiss need in no 
way surprise us, when we picture the variety of materials 
brought by subsidence into the hotter regions of the earth's 
crust, and there subjected to compression in some directions 

* Compare T. G. Bonney, ** Biotito and Hornblende from the Binnenthal," 
Quart. Joum. Oeol. Soc., vol. xlijc tv *2 

2 Geikie and Teall, QitaH, ^o^^ Qefi^' ^"> ^^* ^ ^^^94), p. 657. 



302 OPEN-AIR STUDIES 

and to extension in others, like a red-hot iron bar between 
the rollers of a factory. 

Some gneisses possess a most marked banded stmctnre, 
with sheets of quartz and pink felspar folded in among 
darker and finely grained micaceons layers. Snch cases 
probably result from the metamorphism and rolling ont of 
a region where an igneons rock had penetrated a mass of 
clays ; onr old granite highland may thns some day become 
kneaded up again in the great earth-mill, and only a general 
streakiness in the resulting gneiss will show the original 
complexity of its structure. 

Clays and shales and slates give rise to Kica-SChistS, 
containing varying amounts of quartz and garnet, and per- 
haps a little felspar, according to their original chemical con- 
stitution ; but highly siliceous sediments produce Qnarbdtes. 
Quartzite is the hardest rock ordinarily met with ; it breaks 
across the original sand-grains, and furnishes very angular 
fragments highly suitable for road-metal. Sometimes its 
granular character can be seen with a lens, a cement of 
secondary silica having bound the whole together. This 
cement is deposited in perfect crystalline continuity with 
the grain round which it is formed, and the qnartz-coatings 
of any two grains meet one another in the space between 
them and interlock completely with one another. Hence the 
rock, with the exception of the few impurities that it may 
have contained, becomes a mass of quajtz throughout, and 
the knife can no longer produce any impression on it. 
Qnartz-schist results from the deformation of such a rock, 
as already described (p. 299) ; and the foliation is often aided 
by flakes of mica which were originally present, or which 
have developed from the impurities during metamorphism. 

Limestones, again, become converted by pressure-meta- 
morphism into Crystalline Marbles, all traces of their fossils, 
and often of their original bedding, having disappeared, and 
the rock becoming a mass of closely fitting granules of calcite. 
Streaks of materials which are subsequently carried througli 
them by permeating waters often give marbles additional 
value as ornamental stones. Where a flow has occurred 
under pressure, any impurities present, or capable of pro- 
ducing ciystals, commonly mark out the foliation-planes; 
and thus we have micaceons marbles, which are common in 
the south-west r^ons of the Alps, and marbles with ampbi- 



THE FOLDS OF THE MOUNTAINS 303 

bole, developed in spreading fern-like patches, such as those 
of central Sutherland. Such foliated marbles may well be 
described by the old French name, Calcschist. In meta- 
morphosed limestones, the softness of the calcite, and its 
glancing cleavage- surfaces, will easily serve to distinguish 
the rock from quartzite. 

Crystalline Dolomites also occur, where a limestone has 
been chemically altered, half of its molecules of calcium 
carbonate having been replaced by magnesium carbonate, 
and the mass having then been subjected to pressure-meta- 
morphism. The specific gravity of such rocks is about 2.85, 
a character that will distinguish them from ordinary marbles, 
which give about 2.72. True dolomite, moreover, where the 
replacement has been in the proportion stated above, does not 
eifervesce in cold acid, like ordinary limestone, but only upon 
heating (p. 18). 

Schists sometimes consist of hornblende and granular fel- 
spar in alternating bands (Hornblende-schist), as at the Lizard 
in the south of Cornwall. These, as above hinted, are the 
products of the metamorphism of igneous rocks of the 
"greenstone" or diabase type (p. 208). Chlorite - schists, 
commonly spotted with magnetite, probably also result from 
the alteration of igneous rocks; and Serpentine-schists are 
fairly common among the Alpine ridges, these soft and easily 
squeezed masses arising from the metamorphism of rocks 
once rich in olivine. 

As we go up towards the St. Gotthard Pass by the steep- 
sided valley of the Eeuss, the walls begin to close in, and 
the rocks around us become more coarsely crystalline. At 
Goschenen, where we look up towards snows and glaciers near 
at hand, the bare cliffs of the ravine are formed of a white 
micaceous granite, passing, by development of foliation, into 
gneiss. This is the typical rock of the central Alps, and is 
traversed by huge joint-planes, which often give smooth 
surfaces to the cliffs. The most striking part of the valley is 
between Goschenen and Andermatt, after the great railway- 
tunnel has started beneath us on its nine-mile journey through 
the ridge. An avalanche-gallery protects us from the slip of 
the great jointed blocks of gt'anit©? si^^ ^^® i^^ad winds upward 
in characteristic Alpine C\XY*ve9» ^^ Heuss comes down in 
thunder beneath the Dev^V t^ndge, deluging the road with 
spray ; and at last the soli^ ^ ^otxtory itx iiont has to be bored 



304 OPEN-AIR STUDIES 

through to provide a passage. Suddenly, on the other side of 
it, we emerge upon a long grassy valley, leading westward to 
the Furka Pass. The hills on either side, often snow-covered, 
are smooth, and green with vegetation ; and the chalets of 
Andermatt lie smiling in the entrance of the valley, with the 
ruined tower of Hospenthal upon its little mound beyond. 

We are reminded of the clustering of the villages along 
certain valleys in the Juras; and we have, in fact, now 
come across, 4800 feet above the sea, one of the remaining 
infolds of Mesozoic strata in a deep synclinal of the schists. 

In the grey limestones before Andermatt, corals and sea- 
lilies have been found, and the calcschists extending up to 
Hospenthal contain Lower Jurassic belemnites.^ Similar 
remains, crushed and broken, with unmistakable fragments 
of ammonites, occur on the much frequented pass of the 
Great Scheidegg near Grindelwald, and in numerous other 
places. Above the Great Scheidegg towers the crag of the 
Wetterhorn, in which Jurassic synclinals lie almost horizon- 
tally amid the intense folding of the gneiss. The metamor- 
phism of the Mesozoic rocks has often proceeded so far as to 
convert them into mica-schists, in which all trace of fossils 
is obliterated. 

And now from Hospenthal, probably in cold drifts of 
northern cloud, we turn out of this strange high valley 
towards the sterner masses on the south side of the syn- 
clinal. With windings at first, and then one final bend, the 
road is carried up the flank of a hollow five miles long, a typi- 
cal and desolate upland of the Alps. The summit of the St. 
Gotthard Pass, 6936 feet above the sea, is a little plateau in the 
granite, with a floor of beautifully glaciated rocks. A few chill 
lakelets lie in the hollows, and already denudation has broken 
away many of the ice-worn surfaces upon their margins. 

Here we are, then, upon the central Alpine ridge, the 
great crystalline core which often rises 13000 and 14000 feet 
above the sea, reaching 15730 feet in its south-west pro- 
longation at Mont Blanc. The rocks that compose it are 
exposed, broadly speaking, over an area 550 miles (900 km.) 
long by 40 miles (70 km.) wide ; ^ but the frequent infolds 

^ C. Schmidt, in the '* Livret-guide g^logique dans le Jura et les Alpes,*^ 
1894, p. 151. 

^ See Noe's admirable " Greologische Ubersichtskarte der Alpen '* (Ed. 
Holzers geographisches Institut, Vienna). 



THE FOLDS OF THE MOUNTAINS 30$ 

of far younger masses show how much had to be denuded 
before the core was thus revealed. Pebbles of Alpine gneiss 
and granite occur in the Mesozoic and Cainozoic beds ; and 
hence we know that a great part of these crystalline rocks 
existed, like our imaginary cathedral-floor (p. 296), beneath 
the sheets of the sedimentary rocks which have since been 
crumpled with them. The Miocene conglomerates at St. 
Gallon contain few pebbles from the central gneiss, and vast 
quantities from the former coating of Mesozoic limestones. 
Moreover, specimens of rocks known only near Lugano, on 
the south side of the present chain, occur in these northern 
pebble-beds ; while great erratic blocks lie in the more recent 
surface-deposits of St. Gallen, which have similarly come 
from south of the now lofty Todi range. Hence Swiss 
geologists believe that, in Miocene and even later times, the 
high ridge lay farther south than now, and that the central 
folds of the St. Gotthard and the Bernese Oberland have 
been subsequently upheaved. Such simple observations 
bring before us a tremendous picture of the great wave in 
the earth's crust, travelling from south to north, forcing the 
Mesozoic beds into enormous folds, and finally crumpling up 
even the Miocene conglomerates, until it died down against 
the old massive rocks of southern Germany. 

Whatever, then, may be the age of the rocks forming 
the central core of the Alps, they owe their present elevated 
position to earth-movements which culminated at the close of 
Miocene times. From our crest of vantage, we may perhaps 
now make a general survey of the matter. The Alps, as we 
know them, are later than the humbler Juras, which already 
formed a chain of island-peaks at the end of the Lower 
Cretaceous epoch. The sea lay over Switzerland in Eocene 
times, and extended far across Egypt in the east. The 
Oligocene period opened with an uplifting movement, which 
drove the sea back from Lausanne and central Switzerland, 
but left an inlet on the west reaching up to B§,le ; and this 
movement continued into the Miocene period, giving us 
again fresh-water deposits. Then the sea temporarily re- 
turned, spreading from B§,le and Bern round the Juras, 
and away as far as Paris, \^bil© ^^® central Alps still con- 
tinued to heave themselves aloW^y ^^^^ ^^» contorting the 
Mesozoic strata and sendix^j^ AnV^^ showers ot pebbles along 
the beds of their rapid t..^ ^ a The Tmne axis shifted 



3o6 OPEN-AIR STUDIES 

northward, as we have above described, and the whole 
Alpine lands became dry at the end of the Miocene period, 
the Pliocene being merely represented, as at Dole, by river- 
gravels and allnviams. 

The form of the great Alpine axis, raised nnder the 
influence of pressure from the south-east and south, was 
moulded, like that of the Juras, against older masses ; and 
the range, running from the south of Turin nearly to 
Vienna, is merely part of a great system of mountain- 
chains, all intimately connected, and all of the same com- 
paratively recent age.^ 

Even the old crystalline rocks of the core, in the stress 
of this period of upheaval, have actually renewed their 
youth. Dr. Lawson^ showed in 1888 how the oldest 
gneisses of Canada had become in part remelted at a later 
period, and had flowed like igneous masses into the cracks 
of the overlying beds. This gives us the other end of the 
circle of events, by which a granitic rock may become con- 
verted by pressure and movement into a gneiss. Here it 
has gone back into the granitic condition, and it becomes 
impossible to style it, in this form, one of the oldest rocks of 
the. district In its consolidated igneous offshoots, we are 
bound to say that it is later than the beds into which it 
has intruded. Similar freaks of Nature have now been 
observed by M. Michel Levy in the central masses of Mont 
Blanc.^ The coarse gneiss, often well foliated, of which the 
magnificent walls and aigicilles are composed, has been shown 
to be an intrusive mass, instead of the oldest rock in the 
core of an anticlinal. Down below, this gneiss may be 
connected with the ancient floor of Europe ; but it is un- 
doubtedly, in its present position, younger than the adjoining 
schists, and its foliation may possibly be the result of igneous 
flow (compare p. 301). 

Dr. J. W. Gregory ^ has similarly referred some of the 
gneisses of the Cottian Alps to a very recent date. He 
describes several intrusive junctions, and regards the folia- 
tion as a flow-structure, finding that it is parallel to the 

1 See Suess, " Antlitz der Erde," Band i, p. 303. 

^ '*Greology of the Rainy Lake Region," Oeol, Surv. of Canada^ Annual 
RepoHfor 1887. 

2 See section in De Lapparent, "Traitd de Gh^logie," 3me. ^t, p. 1518. 
^ " The Waldensian Gneisses and their place in the Cottian Sequenoe," 

Quart. Joum, OeoU Soe., voL 1 (1894), p. 232. 



THE FOLDS OF THE MOUNTAINS 307 

walls of the dyke-like offshoots. "The dykes," he writes, 
"often have an irregular course through the schists, but 
the foliation in them remains quite independent of the 
surrounding rocks." Instead of treating this gneissic granite 
as an Archaean mass, as so many authors have done, Dr. 
Gregory is driven to this conclusion : — " Paradoxical though 
it may appear, the evidence renders it most probable that 
the Waldensian gneiss, instead of being of Laurentian ^ age, 
is really Pliocene, and, with the exception of the Saharian 
and recent alluvium and the glacial moraines, is the newest 
rock in the Oottians." 

Such a suggestion will not go by unchallenged ; but the 
idea that schist and gneiss may be manufactured in any 
period of the earth's history is at least a most reasonable 
one, and was familiarly held by many of the older geologists 
when the principles of our science were being established. 
The most important discovery of recent times with regard 
to metamorphic rocks is that the planes of foliation have 
usually nothing to do with the original stratification of a 
sediment ; and this fact has made it more difficult to assign 
a sedimentary origin to this or that group of schists. But 
the alterations in an obvious shale when in contact with 
a granite mass are of a sufficiently convincing character ; 
mica-schists and andalusite-schists are in such cases pro- 
duced, as it were, before our eyes. It is not difficult, then, 
to believe that great thicknesses of schist have been added 
to the crystalline series of the Alps, even during the latest 
movements of the chain. Such movements allowed of the 
intrusion of gabbros and basalts, which became rolled out 
into sheets of homblendic and chloritic schists,^ and of 
granites, which, flowing in under pressure, filled up some of 
the great mountain-domes with gneiss. 

The crystalline core, then, on which we stand at the 
summit of the St. Gotthard Pass is a complex mass of various 
ages, representing the kneading together of many rocks in 
the earth's mill.^ Let us now descend on the southern side 
towards the Italian plain. 

^ Early Archaean. 

* G. Cole, ** Some Problems of the Western Alps ; Sediments, Schists, 
and Greenstones," Proc, London AvrmtCV'T 'Sci* 80c. ^ 1890. 

^ One of the clearest discussiot^^ ^ ^^le problems of pressure- metamorphism 
occurs in Professor Lapworth's ertu? ni Pago'^ " Introductory Text-Book of 
Geology,'' 12th edit. (1888), pp. ^W*^ ^, 



308 OPEN-AIR STUDIES 

The first wonderful curvings of the road, which is but- 
tressed up tier upon tier in the steep head of the Val Tremola, 
bring us across slabs and joint-surfaces of gneissic granite, 
like those of the gorge at the Devil's Bridge. Then, in the 
valley and in the succeeding green and open country, set with 
little woods and rough grassy hollows, we meet exposures of 
fine-grained mica-schists. We have crossed the great central 
fan-fold of the gneiss, and are among the synclinals and anti- 
clinals which lead up to it from the south. The next series 
of schists, rich in lime in one combination or another, are re- 
f eiTed by the Swiss geologists to the Jurassic system. They 
occupy the same position as those with crushed and elon- 
gated belemnites on the passes east and west of us.^ 

At the mouth of the giim Val Tremola, veins of a kind of 
gneiss, occurring in the schists, suggest that here also we 
have evidence of the rolling out of an igneous contact-zone. 
These older schists are beautifully foliated, passing into 
gneiss ; but the far newer rocks of the Jurassic zone also 
consist of a great variety of schists. Though we find here 
in association masses of very different ages, we can under- 
stand how older observers thought they saw a complete pas- 
sage from unaltered sediments to crystalline granite, as they 
went from the exterior to the interior of a mountain-chain. 
And even now the central masses of the Alps may prove to 
have the most recent origin. 

Airolo, of Italian aspect, stands upon this southern infold 
of Mesozoic schists ; one or two other synclinals are caught 
in, and are exposed on the walls of the great valley; and 
then we have a long stretch of somewhat fine-grained 
gneisses, extending right away to Bellinzona. Here the 
rivers from the north have formed a broad alluvial flat, which 
is still occasionally flooded. The rainfall can now no longer 
deepen the valleys, and we see in this spreading of the 
alluvium, creeping back towards the central range, a model 
of those larger processes that have produced the Italian 
plain. A little farther down, we come into the southern 
lake-country, which repeats the features of northern Swit- 
zerland. The elongated winding forms of the " Italian lakes" 

^ A review of the relations of Jurassic rocks and older schists in the Alps, 
from a point of view diflfereut to that here adopted, will be found in Prof. 
Bonney's ** On the Crystalline Schists and their Relation to the Mesozoic 
Rocks in the Lepontine Alps," Quart, Joum. Geol, Soc,, voL xlvi (1890), p. 187. 



THE FOLDS OF THE MOUNTAINS 309 

are easily seen on any map. The Lago Maggiore, thirty-five 
miles long and two miles wide, is clearly the flooded valley 
of the Ticino ; at Pallanza, the mouth of the Toce forms the 
one conspicuous side-inlet. But no ordinary alluvial dam 
has closed the outlet at the southern end ; the whole valley- 
floor must have become curved downwards, giving rise to 
this lake 2800 feet in depth. At present it is partly filling 
up again, and Locarno, at the northern end, stands upon a 
delta of the most exquisitely developed form. 

If we follow the route of the St. Gotthard railway to 
Lugano, we find another group of warped and tilted valleys. 
The Lake of Lugano consists of at least four valleys, and its 
original drainage-lines are difiicult to trace. At present it 
overflows from a western arm into the middle of the Lago 
Maggiore. The three-armed Lake of Oomo presents fewer 
diflSculties ; from north to south, from Ohiavenna to Lecco, 
it forms a fine and gently curving valley; and another 
stream formerly entered this obliquely, from the watershed 
in the neighbourhood of Oomo. It is certainly unusual for 
a tributary to point so distinctly up the valley of the main 
stream ; but there are local examples of this in the un- 
submerged valleys immediately to the north. 

From the Triassic beds of Lugano we can pass to the 
Jurassic of Como, and so to the Cretaceous exposures about 
Lecco. Here even the Eocene sea has left us traces, full of 
nummulites, like those of the northern flank of the Alps. 
But the plain of Italy has covered up most of the Mesozoic 
and Oainozoic beds, and we have to go eastward to find the 
counterpart of the boldly scarped limestone ridges, which 
form the Alpine foot-hills across central Switzerland. 

In among the glacial detritus west of Como, there lie 
patches of marl, containing marine Pliocene fossils. It is 
perfectly possible, and indeed probable, that glaciers de- 
scended from the central ridge, which was then at its full 
height, and mingled their terminal moraines with the de- 
posits of an Italian sea. In any case, the huge earth- 
wave of the Alps rose up, without driving back the sea on 
the south side. Shallowings had occurred in the Italian 
region in early Miocene times, but were followed by renewed 
deepening of the sea along J^g northern shore ; parts of the 
Apennines may have ris^n in ^^ Oligocene and Miocene 
periods, but their main upV «\ actually occurred at the con- 



3IO OPEN-AIR STUDIES 

elusion of the Pliocene. The marine Lower Pliocene series 
lies upon the Apennine slopes, and the active volcanoes of 
western and southern Italy are fair evidence that earth- 
movement is still in progress. The granite core of the 
Apennines is exposed only at its northern and southern 
ends, through the mantle of Cretaceous and Jurassic strata. 
We seem to be carried back, in viewing this modem moun- 
tain-range, to the Alps of Miocene times, before their final 
crumplings and upheavals had taken place. The highest 
point of the Italian range is Monte Oomo in Abruzzo, 9521 
feet above the sea ; and there is no good reason to believe 
that these ridges have ceased growing at the present time. 
Such growth, however, cannot be accomplished without con- 
siderable reduction in the width of the masses which lie at 
present above sea-level, since Professor Heim^ computes 
that the Alps in some parts occupy only half the horizontal 
space formerly required by the sediments that were used up 
in their construction. 

If it seems extraordinary that the Apennines should 
practically be of Post-Pliocene origin, and that all the 
complex peaks and gorges of the Alps should have been 
carved out in them since Miocene times, we have only to 
turn to other mountain-chains to verify these conclusions. 
The principles that guided William Smith cannot here 
deceive us. Nummulitic strata are found infolded with 
the Pyrenees, a range that reared itself in Eocene and early 
Miocene times. The Joras, as we have seen, were not clear 
from the sea until the Miocene period, and are thus some- 
what younger than the Pyrenees and older than the Alpine 
foot-lulls. 

The Himalayas are later than the Cretaceous period, 
and their principal folding occurred between Miocene and 
Pliocene times ; ^ but there is evidence, from the disturbance 
of the Pliocene strata on their flanks, that they continued 
to rise even later, and it is probable that they are still in 
upward motion. 

The Rocky Monntains, again, are of Eocene and later 
age, the western ridges being Pliocene, and younger than the 

1 <<Mechanismas der Gebirgsbildung," Band ii, p. 213. 

^ Griesbach, Mem, Oed. Survey of India, vol xxiii, p. 47; Blanford, 
Medlicott, and Oldham, '* Manual of the Geology of India," 2nd edit., pp. 
467-487. 



THE FOLDS OF THE MOUNTAINS 31I 

eastern plateaus. We have already (p. 116) referred to the 
Post-Pliocene movements of the continental coast in Cali- 
fornia ; and it is equally instructive to realise that the canon 
of the Colorado Eiver, 6200 feet in depth, has been excavated 
since early Pliocene times. 

Even the great chain of the Andes, which is increased 
locally by volcanic cones, is younger than the middle of the 
Cretaceous period. 

Wherever, in fact, we study high mountain-ranges, we 
find them to be of comparatively recent origin. The 
supremacy of the Himalayas, attaining 29000 feet, is only 
secured to them by their youth. The older ranges become 
worn down by denudation, like those of Norway, or, still 
more strikingly, like those of our Scottish highlands and 
of Wales. If we have lost our boldest mountain-chains, 
which once fronted the western ocean in the lordly fashion 
of the Andes, we can at least learn something from their 
bare and dissected remnants. The folds have been worn 
down, and it is dijQScult now to point to the position of the 
central ridge ; but in the west of Sutherland and Eoss-shire 
the phenomena of the overthrusting of more recent sedi- 
ments by crystalline rocks are displayed, as they might be 
on the flank of any modem mountain-chain. In the foot- 
hills of the Alps, the huge folds and thrust-planes can be 
traced out on thousands of feet of precipitous rock ; but it 
is a still more difficult matter to follow out the succession 
of events in our own highlands, where only little flecks and 
patches of some of the largest folds remain. Professor Nicol 
was the first to bring the study of modem mountains to bear 
upon the Silurian range of Scotland ; but the proof of the 
general correctness of his views was left to the detailed 
mapping of Professor Lapworth, nearly thirty years later. 
Professor Lapworth^ showed how thrust after thrust had piled 
up the strata in the Durness district, so that what had long 
been regarded as a regular and conformable succession of 
deposits was proved to be a repeated and often an inverted 
series. His work was extended by the officers of the Geo- 
logical Survey,^ who showed again and again that Archaean 
gneiss overlay little altered Cambrian and Ordovician strata. 

^ "The Secret of the Highlands " ^^^' ^^3"> ^^^3» PP* '^o, 193, and 337. 
* " Report on Recent Work i ' the North- West Highlands of Scotland," 
Quart, Jowm, Oeol, iS'oc.,\vol. xli^ / 1888)» P» 37^ » ®®® especially figs. 8-22. 



312 OPEN-AIR STUDIES 

Similarly startliDg results will probably be obtained in Ire- 
land, now that Professor Lapworth has opened np the way. 
The old continental edge, represented by Norway, the west 
of Satherland, and the outer Hebrides, is continued sonth 
into the counties of Donegal and Galway. Here Archsean 
gneisses and early Palseozoic strata have similarly been 
thrust together, and the bared core of the old mountain- 
range forms the existing and richly varied highlands.^ 

Gneisses and schists have now a new meaning for us, and 
open np some of the most tremendous problems of the stmc- 
tnre and history of the earth's crust While some of these 
rocks represent the flow of deep-seated and once molten 
masses, which, although in motion, had become in great 
part crystalline, others tell us of the fracture and movement 
of rocks already firm and hard. The folds that we see npon 
the coast of Devon or Dorset (Plate XI), with their contor- 
tions and actual reversals of unaltered strata, show how much 
movement may go forward without metamorphism of the 
rocks. But down below ns, and in the heart of an uprising 
mountain-chaiQ, the greater heat and pressure may be manu- 
facturing schists at the present day. The Pyrenees, the 
Western Alps, and the Karpathians, have protebly already 
come to rest. Where will the next range rise to take 
their place, when they have become reduced to denuded 
remnants ? 

The Pliocene or Post-Pliocene elevation of two axes, at 
least, gives us some fair ground for speculation. The Apen- 
nines have already started with considerable success (p. 309) ; 
but the Wealden anticlinal (p. 282) still remains only some 
300 to 800 feet above the sea The Eocene and Oligocene 
rocks have been denuded back upon its flanks, the Cretaceous 
fold has been cut through, and near Hastings the Jurassic 
beds have been brought up and bared upon the surface. So 
far it is mere guess-work to suggest anything more serious 
for the future ; but there are signs of the formation of small 
subsidiary folds within the main limbs of the Wealden anti- 
clinal. Perhaps, after all, the gneiss and granite far below 
will once more see the light of day ; London and Brighton, 
long before lost to human knowledge, and buried in con- 
glomerates from the rising mountain-chain, will become in- 
folded in the recumbent synclinals of the foot-hills, north and 

' See OeoL, Surv, of Irdand, Longitudinal Sections, Sheet 34 (189 1). 



THE FOLDS OF THE MOUNTAINS 313 

south ; and, finally, crowds of regenerate mortals, each one a 
scientific observer from his birth, will flock on public holi- 
days to the snow-peaks of the English Alps. 

And so the folds of the mountains have brought us back 
to our own islands, to Sutherland and Galway, to Dorset 
and the Surrey hills. Our first observations on the form of 
mountain-slopes (p. 28) have led us on and on, until we have 
halted on the border of some of the most mysterious problems 
of the earth. Though we travel, as geologists should, from 
one country to another, we may rest assured that these isles 
of ours contain ample matter for research. Whether we 
cycle along the great through-routes, noting scarp after 
scarp, the Chilterns, the Ootteswolds, Wenlock Edge, until 
we reach the mountain-land of Wales, or whether we walk 
in an afternoon across the open fields around our homes, the 
subjects of our studies are always near us, the material is 
ready to our hands. And if we have journeyed thus far 
pleasantly together, it is perhaps time that we should now 
choose our own work, and our own way of setting about it. 

" And so, without more circumstance at all, 
I hold it fit that we shake hands, and part." 



INDEX 



Actinocaxnax, 273 

Aiguilles, 44 
Airolo, 308 
Alabaster, 18 
Albite, 18 
Albury, 61 
Alcoves, 42 
Aletsch Glacier, 48 
All^e Blanche, 84 
Alluvial flat, 68 
Alluvium, 68, 75, 126, 141, 203 
Almandine, 199 

Alps, the, structure of, 296, &c. ; his- 
tory of, 305 
Ammonites, 237, 266, 270 
Amphiboles, 19 
Amygdaloidal structure, 182 
Ananchytes, 278 
Andalusite, 200 
Andermatt, 304 
Andes, 311 
Andesite, 169 
Anorthite, 19 
Anticlinal, 251 

Antrim, County, 72, 181, 277, 278 
Aosta, 75 

Apennines, 309, 312 
Apparent dip, 248 
Aragonite, 17 
Archaean era, 231, 311 
Ardte, 42 
Arlberg Pass, 64 
Arran, island, 118 
Artesian springs and wells, 60 
Arve, river, 78, 79 
Ash, volcanic, 154 
Ashdown Forest, 246, 255 
Athelney, Isle of, 125 
Atherfield Clay, 260 
Atmosphere, temperature of, 36 



Atoms, 5, 6 
Augite, 19 
Auvergne, 148, 174 
Avalanche, 44 
Axmouth, 72 



B 



BaSff, on River Arve, 78 

Bagshot Heath, 280 

Bale, 289 

Banded structure, 166, 212 

Bargate stone, 263 

Barrois, on Chalk, 269, 273 

Bars of rivers, 90 

Basalt, 169 

Bath, 164 

Bath stone, 236 

Bavarian plain, 128 

Bay, 96 

Beaches formed by storms, 102 

Bedford Level, the, 124 

Belemnitella, 278 

Belemnites, 267, 273, 278 

Belfast, 182, 185 

Belfast Lough, 97 

Bellinzona, 308 

Ben (Beinn) Cruachan, 209 

Ben Nevis, 35, 38, 40, 43 

Beringer, Prof., on supposed fossils, 

223 
Biotite, 20 
Birds, early, 258 
Black Forest, 292 
Blackdown Hills, 268 
Bog iron ore, 142 
Bohemian Forest, 130, 163 
Bombs, volcanic, 152 
Bonneville, Lake, 139 
Bonney, Prof., on rounding of 

pebbles, 78 



314 



INDEX 



315 



Borings under London, 267 

Bothnia, Gulf of, 92 

Bournes, 61 

Box Hill, 247 

Bray, Lough, 56 

Breaching of volcanoes, 160, 176 

Breccia, 287 

Bristol, 236 

Brittleness of minerals, 10 

Brunig Pass, 294 

Budapest, 130 

Burma, remains of early man in, 241 



c 



Gader Idris, 56, 209 

Cainozoic era, 238 

Calcite, 17 

Galcschist, 303 

California, 116 

Cambrian period, 232 

Cambridge, 121, 271 

Cafions, 66 

Cantal, the, 179, 180 

Carboniferous period, 233 

Carlingford Mountain, 210 

Cammoney Hill, 185 

Carrick-a-rede, 185 

Carrickfergus, 185 

Caspian plains, 144 

Caspian Sea, 144 

Casts, 220, 276 

Caves, sea- worn, 95 

Cetiosaurus, 256 

Chalcedony, 16 

Chalk, 237, 269 ; examination of, 272 

Chalybite, 18 

Chamwood Forest, 209 

Chatham boring, 268 

Chemical composition of minerals, 15 ; 

of igneous rocks, 166, 204 
Chenaillet, le, 84 
Chert, 261 
Chesil Bank, 112 
Chiastolite, 200 
China, loss in, 133, 136 
China-clay, 203 
Chisel, stone-mason's, 26 
Chislehurst, 239, 244 
Chlorite, 21 
Chlorite-schist, 303 
Choking of gorge, 75 
Cirque, 42, 56 
Cirrus-clouds, 37 
Clay, 21, 100; examination of 

^^65 



Cleavage of minerals, 14 ; of slate, 

299 
Clermont-Ferrand, 148 
Cliffs, formation of, 98 
Clinometer, 248 
Clouds, 37, 38 
GluseSf 290 
Coalfields, 234 
Coal -Measures, 233 
CW, 85 

Colour of minerals, 9 
Columnar jointing, 172 
Combe, 42 
Como, Lake of, 309 
Compound, chemical, 5 
Concretions, 221, 270 
Cones of dihris, 64, 69, 295 
Cones, volcanic, 157 
Conglomerates, 102 
Constanz, Lake of, 80 
Contact-metamorphism, 199 
Contortion, 283 
Coral-reefs, no 
Cordier's observations on fine-grained 

rocks, 24 
Cortina, 73 
Coruisk, Loch, 57, 211 
Cornwall, 192, 194 
C6te d'Or, 288 
Cotteswold Hills, 236 
Cottian Alps, 306 
Coves, 96 
Crater, 151 
Crater-lakes, 179 
Cretaceous period, 237, 279 
Crevasses, 47 
Cromer, 86, 96 
Cross Ness boring, 267 
Crowborough Beacon, 255 
Croydon, 239 

Crust of the Earth, 3, 22, 151 
Crystals, 8, 12 
Crystal-systems, 13 
CuchuUin Hills, 211 
Current-bedding, 77, 104 
Cushendall, 182 
Cwm, 42 
Cwm-glas, 55 
Cycads, 257 



Dakyns and Teall, on variation in 

igneous rocks, 213 
Dana, on Sandwich Island pumice, 153 
Danube, 88, 128, 130 



3i6 



INDEX 



Dartmoor, 192, 194, 208 

Dead Sea, 143 

Decomposition of granite, 202 

Deltas, 81, 88 

Denudation, 42 

Derbyshire, 233 

Derived crystals, 198 

Desert of Utah, 137 ; of Sahara, 145 

Devonian period, 233 

Dew, 39 

DiabAse, 208 

Diatoms, 108, 11 1 

Diorite, 205 

Dip, 247 

Dip-slope, 250 

Dissolved matter in rivers, 90 

Dole, 288, 292 

Dolgelley, 232 

Dolomite, 18, 303 

Dorking, 244 

Dorsetshire, 264 (see Lulworth) 

Doubs, river, 288 

Dover, Straits of, 97 

Down-throw, 285 

Drau, river, 70, 132 

Drift, 240 

Dudley, 232 

Duich, L<x!h, 117 

Dunge Ness, 112 

Durness, 311 

Dust, volcanic, 153 

Dykes, 158, 173 

E 

Earth-pyramids, 78 

Earthquakes, 287, 296 

EchinoconuR, 278 

Edinburgh, 186 

Eiflfel Tower, 36 

Elasticity of minerals, 11 

Element, chemical, 4 

Elements, proportion of, in earth's 

crust, 22 
Elephas, 288 
Elm, 72 

English Channel, 97, 99, 1 19 
Eocene period, 238, 280 
Eras, 229, 241 
Erratics, 51 

Eruption of volcanoes, 151 
Escarpments, 250 
Estuarine deposits, 90 
Etive, Loch, 117 
Etna, 159 
Evaporation, 37 



Exe, river, 234 

Exeter, 271 

Extinction of volcanoes, 162 ; of 

species, 225 
Extraction of particles from powdered 

rock, 23 



Fair Head, 185 

Fall of mountain-rivers, 79 

Fans of dibris, 69, 126 

Fan -structure, 283 

Fault-rock, 287 

Faults, 285 

Fauna, 226 

Felspars, 18, 19 

Fenland, the, 121 

Ferret, Cape, 11 1 

Ferro, Valle del, 65, 125 

Finchley, 56 

Fim, 45 

Fim-ice, 45 

Fjords, 116 

Flexibility of minerals, 1 1 

FUms,73 

Flint, 16, 261, 274 

Floods in rivers, 64 

Flora, 226 

Flow of compressed strata, 288 

FluidaJi structure, 165, 212 

Fluorspar, 194 

Fluviatile deposits, 90 

Folded strata, 283 

Foliation, 300 

Folkestone Beds, 265 

Foot-hills, 126 

Footprints, 104, 222 

Foraminifera, 106, no 

Forest of Dean, 234 

Fosdyke, 121, 122 

Fossils, 220 ; stratigraphical value 

of, 226 
France, Cretaceous beds of, 278 
Fresh water, 90 
Frozen water, effects of, 41 
Fumaroles, 163 
Fyne, Loch, 117, 118 

G 

Gabbro, 205 

Granges, 88, 134 

Gardiner, Miss, on oontact-meta- 

morphism, 200 
Garnet, 199 



INDEX 



317 



Garron Tower, 72 

Gases in volcanoes, 162 

Gault, 265 

Geikie, Sir A., on volcanic action in 

British Isles, 187 
Gemmellaro, Monte, 159 
Genera, 225 

Geneva, Lake of, 141, 295 
Geology, science of, 2 
Geysers, 164 

Giant's Causeway, the, 173 
Giants' Kettles, 32 
Glacial epoch, 239 
Glaciation, 51, 304 
Glacier- garden at Lucerne, 32 
Glacier- grains, 45 
Glacier-mills, 52 
Glaciers, 46 ; advance and retreat of, 

48 ; movement of, 46, 48 
Glass, volcanic, 165, 166 
Glauconite, 107, 263 
Glencullen, 78, 86 
Glendalough, 81 
Globigerina, ill 
Gneiss, 298, 301, 306 
Godstone, 254 
Gohna landslip, 74 
Goodwin Sands, 97 
Gorges, 34, 66 
Goschenen, 303 
Graham's Isle, 162 
Grand Sarcouy, 178 
Granite, 3, 189, 204 ; origin of, 

195 
Great Basin, the, 136 

Great Salt Lake, 137 

Greece, fossil mammals of, 240 

Greensands, 107, 263, 269 

Greenstones, 209 

Gregory, J. W., on Cottian Alps, 

306 

Grivola, the, 53 

Ground-moraine, 51 

Groups of strata, 229, 23 1 

Guettard, on Auvergne, 174 

Guildford, 246 

Gypsum, 18, 142 



Hag^e and Iddings, on igneous 

rocks, 196 
Hammer, geological, 26 
Hanter h3i, 209 
Hardanger Fjord, 117 



Hardness of minerals, 10 ; of minute 
grains, determination of, 10 

Harker, on the Shap granite, 201 

Harting Combe, 246, 252 

Hdbert, on Chalk, 273 

Hebrides, inner, 239 (see Skye) ; 
outer, 231 

Heim, on landslips, 72 ; on compres- 
sion of Alps, 310 

Heligoland, 98 

Himalayas, 3 10 ; glaciers of, 48 

Hindhead, 245 

Hoar-frost, 39 

Hog's Back, the, 246, 253 

Hohe Tauem, 44 

Holaster, 277 

Holkbam, 228 

Holland, 124 

Holland, T. H., on Gohna landslip, 75 

Holt Fleet, 32 

Hoplites, 266 

Hornblende, 19 

Hornblende-schist, 303 

Hospenthal, 304 

Hot springs, 162, 163 

Hourn, Loch, 117 

Howth, 74, 287 

Hume, W. F. , on Chalk, 272, 273 

Hungarian plain, 130 

Hutton, Jas., on granite, 198 

Hythe, 112 

Hythe Beds, 260 



Icebergs, 50 

Ice-cave, 47 

Ice-fall, 47 

Igneous rocks, 156; table of, 206; 

variation in, 213 
Iguanodon, 256 
Impermeable rocks, 59 
Imst, 70 

Indian plain, 134 
Inoceramus, 274 
Intrusive sheets, 158 
Ireland, Cretaceous beds of, 279 
Irish Channel, 118 
Iron Pyrites, 17 
Isar, river, 128 

Islands, volcanic, 162*, formed by 
submergence, i\7 

Isle of ^Igbt, 9^, 22/v, 239 

Italiaix Ultes, 3,0% \ ^lavti, i^Si 127. 
309 



3i8 



INDEX 



Joints in rocka, 34, 66, 9S, 172. 

190,288 
Jolj, on foaibilitj of minerals, 152 
Jottlan, river, 143 
Jndd, on water in laras, 156; on 

relations of igneoos rocks, 196 ; on 

Oligocene strata, 239 
Jumna, river, 135 
Jara Mountains, 236, 289, 310 
Jnrassic period, 236, 304 



Kammerbiihl, the, 163 
Kaolin, 21, 202 
Karinthia, 62 
Karlsbad, 164 
Karpathians, 131, 312 
Kenmare, 57 

Kentish Town boring, 267 
Kiel, 92 

Kilaoea, 156, 158 
Krakatoa, 154, 161 



Ijabradorite, 19 

Lago Maggiore, 309 

Lahontan, Lake, 141 

Lakes, formed by earth-movement, 

295 ; in cirques, 34 ; in craters, 

179 ; salt, 137-145 
Lake-floors, 140 
Landslides, 70 
Landslips, 71 

Lapworth, on Damess strata, 311 
Larne, 143, 181 
Lavas, 151 ; chemical composition of, 

164 ; mineral constitution of, 168 ; 

classification of, 171 
Lava-cones, 157, 178 
Lava-streams, 155 
LawBon, on Canadian gneiss, 306 
Leinster chain, 208 
Leith Hill, 61, 244, 257 
Lenham, 281 

L^vy, on Mont Blanc, 306 
Lienz, 70 
Liffey, river, 79 
Lignite, 102 

Limestone, 17, 4i» 109, 142 
Limestone-mud, 109 



Limonite, 16, 142, 257 

Linear grooping of ccMies, 159 

Lipari Tslandw, 154, 166 

Lismore, 64 

Lianiore, island, 117 

Llanberis, 53, 55, 187 

Llangollen, 57, 64 

Lnam, 100 

Long, Loch, 117 

Ldes, 133 

Lower Chalk, 269 

Lucerne, glacier-garden, 32, 53 ; Lake 

of, 294 
Lugano^ Lake of, 309 
Lulworth, 96, 258, PL xi 
Lustre of minerals, 10 
Lyell, 00 Cainoxoic beds, 238 



Kagnetisin of minerals, 15 

Magnetite, 16 

Maidstone, 256 

Malleability of minaala, 10 

Malvern, 231 

Mammals, of British Isles, 1 19 ; 
early types, 237, 260; Uter types,' 
240 

Man, eariy, 240, 242 

Mantell, on Iguanodon, 256 

Marbles, 17, 302 

Marcasite, 17, 270 

Marine deposits, 90, loi 

Marl, loi 

Marr, on the Shap granite, 201 

Marten, H. J., on river-erosion, 32 

Matterhom, 44, 53, 56 

Megalosaurus, 256 

Melboum Rock, 273 

Mendip Hills, 233 

Merstham, 244, 254 

Mesozoic era, 236 

Mestre, 88 

Metamorphism, 199, 298 

Metric weights and measures^ rela- 
tions of, 1 1 

Mica, 8, 20 

Mica-schist, 302 

Micraster, 278 

Middle Chalk, 271 

Mineral, definition of, 9 

Mineral waters, 163 

Minerals, observation of, 3 

Miocene period, 238, 239, 293 

Mississippi, 88 



INDEX 



319 



Moelwyn, 56, 187 

Mole, river, 253 

Molecules, 5 

Mont Blanc, 44, 50, 53, 79, 84, 304, 

306 
Mont Dore, 179 
Moraines, 49, 51 
MoulinSf 52 

Mountains, denudation of, 28, et seq. 
Mountain-chains, curvature of, 292, 

306 
Mountain-ranges, 283, et acq, 
Mourne Mountains, 39, 192, 208 
Mud, 100 
Muir Glacier, 46 
Muscovite, 20 
Mynydd-mawr, 187 



N 

Nautilus, 240, 270 

Neocomian, 279 

Ness, Loch, 296 

Neuch4tel, 278, 290 

Nevada, 136, 141, 196 

N^v^, 45 

Newhaven, 99 

Nicol, on highland gneiss, 311 

Nile-delta, 89 

Noetling, on early man, 241 

Norfolk, 239, 267 

North America, lakes of, 295 

North Downs, 245, 249 

North Sea, 92, 119, 122 

Norway, 116 

Nucula, 267 

Nummulites, 293 

Nummulitic strata, 294, 310 

Nuovo, Monte, 160 



Obsidian, 166 
OchU Hills, 186 
Oligocene period, 238, 239 
Oligoclase, 19 
Olivine, 20 
Olivine-Gabbro, 205 
Oolite, Oolitic limestone, no 
Oolitic grains, 1 10 
Ooze, III 
Opal, 16 
Orbitoides, 293 
Ordovician period, 232 



Orthoclase, 6, 14, 18 
Outcrop, 252 
Overlap, 219 
Overstep, 218 



Palaeozoic era, 232 

Faludina, 255, 288 

Paris Basin, 238, 239, 288 

Pass, 85 

Peaks, 42, 43, 53 

Peat, 123 

Pebble-banks, 100 

Pebble-beds, 102 

Pecten, 225, 270 

Pennine Chain, 234 

Perched blocks, 53 

Periods of past time, 229, 231 

Perlitic structure, 174 

Permeable rocks, 58 

Permian period, 234 

Pemter, Dr. , on avalanches, 44 

Pevensey, 112 

Phosphatic deposits, 271 

Piave, river, 127 

Pinnacles of rock, 43, 44, 192 

Pipes, 281 

Plagioclase felspars, 19 

Plain of marine denudation, 95 ; of 

northern Europe, 133 
Plains, 121, et seq. 
Plateaus of lava, 183 
Pliocene period, 238, 239 
Plymouth, 233 
Po, river, 88 
Pocket-lens, 26 
Polished surfaces of rocks, value of, 

in examination, 24 
Pontarlier, 290 
Porcupine Bank, 120 
Porphyries, 167 
Porphjndtic structure, 167 
Portland stone, 221, 237 
Portrane, 113 
Post-Pliocene period, 239 
Pot-holes, 30-32 
Pumice, 153 
Purbeck Marble, 255 
Pay de Cdme, 150; de D6me, 148, 

178 ; des Goules, 150; de Lassolas, 
176 ; de Loucbadi&e, 175 ; Mary, 
180 •, dePat\o\i, 149 •, delaYache, 
176 



320 



INDEX 



Pyrite, 17 

Pyroxene- Di*»rite, 205 

P^'rvxeneif, 19 



Quartz, 6, 16 
(^nartz-Diorite, 203 
C^iartzite, 302 
Quartz-BchUt, 302 



B 



Badiolariang, 108 

lUin, 37 ; ga^eri in, 40 ; chemical 

action of, 40 
Rainfall, 39 
Rain-gauges, 39 
Rain-prints, 222 
Raised beaches, 1 1 5 
Recumbent folds, 284, 297 
Reid, Clement, on Lenham beds, 

282 
Replacement, chemical, 7 
Reptiles, 235, 238, 256 
Reyer, on Schlossberg, 178 
Rhine, river, 47, 79, Sio, 124 
Rhombic pyroxenes, 20 
Rhone, glacier, 47 ; river, 47, 295 
Rhyolite, 168 

Richmond boring, 264, 267 
Richthofen, von, on loss, 133 
Rigi, the, 296 
Ripple-marks, 104, 222 
Rivers, shifting of course, 68, 132, 

135 
River-channels traversing ridges, 85, 

253 
River-erosion, 34, 130 

River-mouth, 87 

Roches moutonn^cs, 52, 54 

Roche Sanadoire, 179 

Rock, definition of, 15 

RockiB, observation of, 2, 3 

Rockall, 120 

Rock-salt, 17, 142 

Rock-sections, preparation of, 25 

Rocky Mountains, 310 

Rossberg, 73 

Ross-shire, 82 

Russell, J. C, on Lake Lahontau, 

141 



I 



s 



►, 145 

St. Gallen, 293 

St. Gotthard Pa8», 296, J03, 504 

St. Leonard's Forest, 253, 255 

Salins, 289 

Salisbury Plain, 237, 250 

Salt lake*, 137-145 

Salts in sea-water, 91, 92 ; in plains, 
136 

Sands, source of, 203 

Sand- banks, 89 

Sand-dunes, 112, 131, 146 

SandsUme, 3, 105. 

Sandwich Islands, 153, 156, 166. 

Saone, river, 288 

Saturation-point of air, 37 

Schist, 298 

Scoriaceous structure, 153 

Scoriae, 153 

Scotland, Cretaceous beds of, 279 

Scrabo Hill, 185 

Scratched stones, 53, 54 

Scrope, on Auvergne, 175 

Sea, salts in, 91 ; gases in, 92 ; ero- 
sion by, 93 

Sea-scorpions, 235 

Sea-stacks, 92 

Sea-water, deposition of solids in, 
88 

Secondary crystallisation, 187 ; mine* 
rals, 182, 300 

Section, geological, 30 

Sedgemoor, 124 

Separation of constituents of rocks, 

23, 77, 105 
Serpentine, 20 

Serpentine-schist, 303 

Severn, river, 32 

Shale, 100, 298 

Shap granite, 194, 201 

Shiel, Glen, 82, 117 

Shore-lines, 87, et seq, 

Sicily, 116 

Sieves for separation, 105 

Sifting of sand, 105, 266 

Silent Pool, the, 61 

Silica, 6 

Silurian period, 232 

Siwdlik Hills, 240 

Skagerrak, 92 

Skeleton-crystals, 165 

Skerries, 218 

Skertchly, on the Wash, 123 



INDEX 



321 



Skiddaw, 200 

Skye, Isle of, 183, 186, 208, 210, 

212 
Slate, 298 
Slemish, 185 
Smith, William, 226 
Smith, Worthington, on tumulus, 

222 
Snowdon, 42, 55, 187, 232 
Snowfields, 44 
Snow-level, 37 
Snow-line, 38 
Soda-pyroxenes, 20 
SoUas, on variation in igneous rocks, 

214 
Solothum, 292 
Solution, materials held by rivers in, 

90 ; by sea, 91 
Soundings off British Isles, 1 18 
South Downs, 246 
Spearing, H. G., on marine erosion, 

97 
Species, 225 

Specific gravity, 11 ; of sea-water, 

91, 92 
Spheroidal structure, 173 
Spherulites, 165 
Spicules of sponges, 262 
Spliigen road, 45, 66 
Sponges, 108, 262, 270, 275 
Springs, origin of, 59 ; mineral, 

163 
Stacks, 92 
Stafifa, 172 

Stratification, 77, 109 
Stratified rock, 76 
Stratigraphical geology, 228 
Stratum, strata, 76, 104 
Streak, 11 

Streams, erosion by, 34 
Striated stones, 54 
Strike, 251 
Styria, 82 

Suess, on earth-movements, 297 
Suffolk, 228, 239 
Sun-cracks, 104, 222 
Sunken land off Ireland, 1 19 
Surrey, 244 

Suspended matter in rivers, 90 
Sussex marble, 255 
Sutherland, 311 
Syenite, 205 

Symmetry of crystals, 13 
Synclinal, 251 
Systems of crjrstallisation, lo ^ 

strata, 229, 231 * ^{ 



Tabular jointing, 190 

Tagliamento, river, 127 

Talus, 35, 63 

Tarns of mountains, 34 

Teall and Dakyns, on variation^ in 

igneous rocks, 213 
Temperature in earth's crust, 152*; 

in lava-streams, 156 
Teplitz, Schlossberg of, 178 
Terebratula, 274, 282 
Thrust-planes, 286 
Thun, 293 

Time-scale of geological eras, 241 
Tisza, river, 131 
Titlis, the, 294 
Toblach, 71, 81 
Topaz, 194 
Tors, 191 

Totlands Bay, 224 
Tourmaline, 194 
Trachyte, 169 

Transparency of minerals^ 10 
Triassic period, 236 
Trilobites, 234 
Tufa, calcareous, 142 
Tuflfs, 153 

Tumford boring, 267 
Twinning of crystals, 13 
Tyrol, 62, et seq. 



Unconformity, 216 
Underground waters, 61 
Upper Chalk, 277 
Upper Greensand, 269 
Up-throw, 285 
Utah, 136 



Val Tremola, 308 

Valleys, 58, et 8eq. 
Variation in igneous masses, 213 
Veins, volcanic, 158 
Venetia, 126 

Venice, 88 

Vesuvius, 160 

Via M.a\a, (i6, ^ . . , 

-Vogt, oti ^,j.xV«A.\.«v Yiv \«Tieoxia xocks. 



322 INDEX 



VolcMioei, 151 ; ■kractare of, 160 
VotgM, the, 289 
Volcano, 154 



Walen. Lake of. So 

Waih, the, 122 

Water, expansion of, on freedng, 41 

Watershed, 84 

Weald, the, 246 

Wealden series, 255, 312 

Wenlock EdgCt 232 

Westward Ho, 97 



Wey, river, 254 

Whitby, 221 

White limestoBe of Co. Antrim 

Wind, velocity of, at high altitndea, 

Wind-action on sand-gxaina, 146 
Windgalle, the, 297 
Worm-boRows, 222 



Zcm0«9 230 
Zng, Lake of, 295 



THR END 



PritUid by Ballantynb, Hanson & Co. 
Edinburgh and London